Ionic Liquid, Lubricating Agent, and Magnetic Recording Medium

ABSTRACT

A lubricating agent including an ionic liquid formed from a Bronsted acid (HX) and a Bronsted base (B), wherein the Bronsted base has a linear hydrocarbon group having 10 or more carbon atoms and the difference between the pKa value of the Bronsted acid in water and the pKa value of the Bronsted base in water is 12 or more.

TECHNICAL FIELD

The present invention relates to an ionic liquid comprised of a Bronstedacid and a Bronsted base, a lubricating agent containing the ionicliquid, and a magnetic recording medium using the lubricating agent.

BACKGROUND ART

Conventionally, in a thin film magnetic recording medium, a lubricatingagent is applied onto a surface of a magnetic layer in order to reducefriction and wear between a magnetic head and a surface of the medium.An actual film thickness of the lubricating agent is at the molecularlevel in order to avoid adhesion such as stiction. Therefore, it's noexaggeration to say that the most important thing in the thin filmmagnetic recording medium is to select a lubricating agent havingexcellent wear resistance under every environment.

It is important to allow the lubricating agent remain on the surface ofthe medium without detachment, spin-off, or chemical deteriorationthroughout a service life of the magnetic recording medium. The moredifficult it is to allow the lubricating agent remain on the surface ofthe medium, the smoother the surface of the thin film magnetic recordingmedium is. This is because the thin film magnetic recording medium hasno ability for replenishing the lubricating agent, unlike a coating typemagnetic recording medium.

In the case where the lubricating agent is only weakly adhered to aprotecting film on the surface of the magnetic layer, a large quantityof lubricating agent is required because the film thickness of thelubricating agent is decreased upon heating or sliding to therebyaccelerate wear. The large quantity of lubricating agent results in amigrating lubricating agent which can have the ability for replenishingthe lubricating agent removed through wear. However, there is a dilemmathat an excess of lubricating agent causes the film thickness of thelubricating agent to be greater than surface roughness to thereby causea problem related to adhesion, and eventually the stiction contributingto drive failure, which is fatal. The problem related to friction hasnot been satisfyingly solved by conventional perfluoropolyether (PFPE)based lubricating agents.

Particularly, in a thin film magnetic recording medium having highsurface smoothness, a novel lubricating agent has been molecularlydesigned and synthesized in order to solve the trade-off. Many reportson a lubricating property of PFPE have been submitted. Thus, thelubricating agent is very important for the magnetic recording medium.

Table 1 shows chemical structures of representative PFPE basedlubricating agents.

TABLE 1 Fomblin based lubricating agentsX—CF₂(OCF₂CF₂)_(n)(OCF₂)_(m)OCF₂—X (0.5 < n/m < 1) Z X = —OCF₃ Z-DOL X =—CH₂OH Z-DIAC X = —COOH Z-Tetraol X = —CH₂ OCH₂CHCH₂OH     OH AM2001

Other lubricating agents A20H

Mono F—(CF₂CF₂C₂O)₁—CF₂CF₂CH₂—N(C₃H₇)₂

Z-DOL in Table 1 is one of commonly used lubricating agents for thinfilm magnetic recording media. Z-tetraol (ZTMD) is those in which afunctional hydroxyl group is additionally introduced in a main chain ofPFPE, which has been reported to enhance reliability of the drive whilereducing gap of a head-media interface. A20H has been reported toprevent the main chain of PFPE from being decomposed by a Lewis acid ora Lewis base, and improve tribological characteristics. Meanwhile, Monohas a different polymeric main chain and polar group from the abovedescribed PFPE, that is, polynormal propyloxy and amine, respectively;and has been reported to decrease adhesive interactions in near contact.

However, a common solid lubricating agent which is believed to have ahigh melting point and thermal stability interferes with highlysensitive electromagnetic conversion process and deteriorates wearcharacteristics due to wear debris produced in a running track when theagent is scraped by the head. The liquid lubricating agent as describedabove has a migrating property which is an ability in which alubricating agent removed through wear is replenished with a lubricatingagent migrated from the adjacent lubricating layer. However, due to themigrating property, the lubricating agent is decreased by spin-off fromthe surface of the disk during disk operation especially under a hightemperature, so that a protective function is lost. Therefore, alubricating agent having high viscosity and low volatility has beensuitably used, which allows for low evaporation rate and long servicelife of the disk drive.

In view of these lubricating mechanisms, a low friction and low wearlubricating agent used in the thin film magnetic recording medium isrequired to have the following requirements:

(1) low volatility;(2) low surface tension for surface replenishing ability;(3) interaction between a terminal polar group and a surface of a disk;(4) high thermal and oxidative stability to prevent decomposition or adecrease during use;(5) chemically inert to metal, glass, and polymer, and no wear debrisproduced by a head or a guide;(6) no toxicity or flammability;(7) excellent boundary lubricating property; and(8) solubility in organic solvents.

Recently, an ionic liquid has been attracting attention as one ofenvironmental friendly solvents for synthesizing organic or inorganicmaterials in electricity storage materials, separation technologies, andcatalyst technologies. The ionic liquid is broadly categorized into amolten salt having a low melting point, and generally refers to themolten salt having the melting point of 100° C. or lower. Importantproperties of the ionic liquid used as the lubricating agent include lowvolatility, no flammability, thermal stability, and excellentsolubility. Therefore, the ionic liquid is expected to be applied as anovel lubricating agent under an extreme environment such as in vacuumor in a high temperature due to its characteristic. It has also beenknown that use of the ionic liquid in a gate of a single self-assembledquantum dot transistor improves the controllability of the transistor bya factor of one hundred over a conventional one. In this technique, theionic liquid forms an electric double layer and serves as an about 1nm-thick insulating film to thereby obtain a large electric capacity.

For example, use of a certain ionic liquid may reduce friction and wearon a metal or ceramic surface in comparison to a conventionalhydrocarbon based lubricating agent. For example, it has been reportedthat, in the case where an imidazole cation based ionic liquid issynthesized by replacing with a fluoroalkyl group, and alkylimidazoliumtetrafluoroborate or hexafluorophosphate is used on steel, aluminium,copper, single crystal SiO₂, silicon, or sialon ceramics (Si—Al—O—N), itshows more excellent tribological characteristics than cyclicphosphazene (X-1P) or PFPE. It has also been reported that an ammoniumbased ionic liquid reduces friction in from elastohydrodynamic toboundary lubrication region compared with a base oil. In addition, anionic liquid has examined for an effect as an additive for the base oil,or researched on a chemical and tribological chemical reaction in orderto understand its lubricating mechanism. However, there are fewapplication examples as the magnetic recording medium.

Among ionic liquids, a protic ionic liquid is a generic designation ofcompounds formed through a chemical reaction between a Bronsted acid anda Bronsted base in equal amounts. Research by Kohler et al. related toan interaction between carboxylic acid and amine has been reported a 1:1complex of carboxylic acid and amine in chemically equal amounts can beformed (e.g., see NPLs 1 and 2). Perfluorooctanoic acid alkyl ammoniumsalt is the protic ionic liquid (PIL), and has been reported to have aneffect of reducing friction in the magnetic recording mediumsignificantly higher than the above described Z-DOL (see, PTLs 1 and 2,and NPLs 3 to 5).

However, these perfluorocarboxylic acid ammonium salts have a weakinteraction between a cation and an anion in the reaction shown by thefollowing Reaction scheme (A). Therefore, the equilibrium is shiftedtowards left side under a high temperature in accordance with LeChatelier's law to thereby produce dissociated neutral compounds,leading to thermal instability. That is, proton transfer occurs underthe high temperature and the equilibrium is shifted towards the neutralsubstance to thereby dissociate (e.g., see NPL 6).

C_(n)F_(2n+1)COOH+C_(n)F_(2n+1)NH₂⇄C_(n)F_(2n+1)COO⁻H₃N⁺C_(n)H_(2n+1)  (A)

The limit of a surface recording density of a hard disk is said to be 1Tb/in² to 2.5 Tb/in². At present, the limit is being approached, butenergetic development has been continued for increasing a capacity onthe assumption of refining magnetic particles. The technologies forincreasing the capacity include decreasing effective flying height orintroducing Shingle Write (BMP).

Additionally, “Heat Assisted Magnetic Recording” is known as anext-generation recording technology. FIG. 3 is a schematic viewillustrating the heat assisted magnetic recording. In the technology, arecording portion is heated with laser upon recording/reproduction, andtherefore, there is a problem that durability is deteriorated due toevaporation or decomposition of the lubricating agent on a surface ofthe magnetic layer. In the heat assisted magnetic recording, themagnetic recording medium may be exposed to a high temperature which issaid to be 400° C. or higher even in a short time. Therefore, commonlyused lubricating agents for the thin film magnetic recording media,Z-DOL and a carboxylic acid ammonium salt based lubricating agent, areconcerned about their thermal stability.

The ionic liquid is generally a substance having high thermal stabilitybecause it forms ions as described above. The equilibrium thereof isshown in the following Scheme 1.

In the above Scheme, HA denotes a Bronsted acid, and B denotes aBronsted base. The acid (HA) and the base (B) react with each other asshown in Scheme 1 to thereby form a salt (A⁻HB⁺).

Herein, the dissociation constants K_(a1) and K_(b2) of the acid and thebase can be shown by the following Scheme 2 using concentrationsthereof.

The K_(a1) and the K_(b2) vary widely depending on substances, and, insome cases, they have the large number of digits. However, the largenumber of digits is inconvenient for handling, so that it is oftenexpressed as the negative common logarithm. That is, as shown in thefollowing Scheme 3, it is defined that −log₁₀ K_(a1) is equal topK_(a1). Obviously, the smaller pK_(a1) is, the stronger the acidity is.

Next, the difference between the dissociation constants of the acid andthe base, ΔpKa, will be discussed. A reaction between an acid and a baseis influenced by their acidity or basicity (or acidity of a conjugateacid), and the difference of acidity ΔpKa can be shown by the followingScheme 3.

As can be seen from the above Scheme, the ΔpKa becomes larger as thesalt concentration [A⁻HB⁺] becomes larger relative to the acid and baseconcentrations.

In particular, Yoshizawa et al. have been reported that, when thedifference between the pKa value of the acid and the pKa value of thebase (ΔpKa) is 10 or more, the proton transfer is more likely to occur,and

[AH]+[B]⇄[A⁻HB⁺]

the equilibrium is shifted towards an ion side (right side) to therebyenhance stability (e.g., see NPL 6). However, MacFarlane et al. havebeen reported that the proton transfer occur and an ionized PIL can beobtained as long as the ΔpKa is at least 4 (e.g., see NPL 7). Dai et al.have been described that, based on an energy level diagram, thermalstability of the protic ionic liquid can be greatly improved bycombining a strong acid with a strong base (e.g., see NPL 8). Watanabeet al. have reported that proton transferability and thermal stabilityof the protic ionic liquid greatly depend on ΔpKa, and, therefore, whenDBU (1,8-diazabicyclo[5.4.0]undec-7-ene) is used as the base, the ionicliquid is greatly improved in the thermal stability by using an acidhaving a pKa value so as to give the ΔpKa of 15 or more (e.g., see NPL9). However, it has not been sufficiently discussed what level of ΔpKais required for a certain application.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent (JP-B) No. 2581090-   PTL 2: JP-B No. 2629725

Non-Patent Literature

-   NPL 1: Kohler, F., Atrops, H., Kalall, H., Liebermann, E., Wilhelm,    E., Ratkovics, F., & Salamon, T., (1981a). Molecular Interactions in    Mixtures of Carboxylic acids with amines. 1. Melting Curves and    Viscosities, J. Phys. Chem. Vol. 85, No. 17, (August 1981), pp.    2520-2524, ISSN: 0022-3654-   NPL 2: Kohler, F., Gopal, R., Goetze, G., Atrops, H., Demiriz, M.    A., Liebermann, E., Wilhelm, E., Ratkovics, F., & Palagyl, B.,    (1981). Molecular Interactions in Mixtures of Carboxylic acids with    amines. 2. Volumetric, Conductimetric, and NMR Properties, J. Phys.    Chem. Vol. 85, No. 17, pp. 2524-2529, ISSN: 0022-3654-   NPL 3: Kondo, H., Seto, J., Haga. S., Ozawa, K., (1989) Novel    Lubricants for Magnetic Thin Film Media, Magnetic Soc. Japan, Vol.    13, Suppl. No. S1, pp. 213-218-   NPL 4: Kondo, H., Seki, A., Watanabe, H., & Seto, J., (1990).    Frictional Properties of Novel Lubricants for Magnetic Thin Film    Media, IEEE Trans. Magn. Vol. 26, No. 5, (September 1990), pp.    2691-2693, ISSN: 0018-9464-   NPL 5: Kondo, H., Seki, A., & Kita, A., (1994a). Comparison of an    Amide and Amine Salt as Friction Modifiers for a Magnetic Thin Film    Medium. Tribology Trans. Vol. 37, No. 1, (January 1994), pp. 99-105,    ISSN: 0569-8197-   NPL 6: Yoshizawa, M., Xu, W., Angell, C. A., Ionic Liquids by Proton    Transfer: Vapor pressure, Conductivity, and the Relevance of ΔpKa    from Aqueous Solutions, J. Am. Chem. Soc., Vol. 125, pp. 15411-15419    (2003)-   NPL 7: Stoimenovski, J., Izgorodina, E. I., MacFalane, D. R.,    Ionicity and proton transfer in protic ionic liquids, Phys. Chem.    Chem. Phys., 2010, Vol. 12, 10341 Luo, H., Baker, G. A., Lee, J. S.,    Pagni, R. M., Dai, S., Ultrastable Superbase-Derived Protic Ionic    Liquids, J. Phys. Chem. B Vol. 113, pp. 4181-4183 (2009)-   NPL 8: Luo, H., Baker, G. A., Lee, J. S., Pagni, R. M., Dai, S.,    Ultrastable Superbase-Derived Protic Ionic Liquids, J. Phys. Chem. B    Vol. 113, pp. 4181-4183 (2009)-   NPL 9: Miran, M. S., Kinoshita, H., Yasuda, T., Susan, M. A. B. H.,    Watanabe, M., Physicochemical Properties Determined by ΔpKa for    Protic Ionic Liquids Based on an Organic Super-strong Base with    Various Bronsted Acids, Phys. Chem. Chem. Phys., Vol 14, pp.    5178-5186 (2012)

SUMMARY OF INVENTION Technical Problem

As described above, in the art of magnetic recording media, there stillremains drawbacks with regard to practical characteristics such asrunnability, wear resistance, and durability due to deficiency inperformance of a lubricating agent.

The present invention has been made in view of the foregoing, andprovides an ionic liquid having an excellent lubricating property evenunder a high temperature, a lubricating agent having an excellentlubricating property even under a high temperature, and a magneticrecording medium having an excellent practical characteristic.

Solution to Problem

The present inventors conducted extensive studies, and have found thatthe aforementioned objects can be achieved by defining, in an ionicliquid, the number of carbon atoms in a hydrocarbon group of a Bronstedbase and a difference between a pKa value of a Bronsted acid and a pKavalue of the Bronsted base. Thus, the present invention have beencompleted.

<1> A lubricating agent, including:

an ionic liquid formed from a Bronsted acid (HX) and a Bronsted base(B),

wherein the Bronsted base has a linear hydrocarbon group having 10 ormore carbon atoms, and

wherein a difference between a pKa value of the Bronsted acid in waterand a pKa value of the Bronsted base in water is 12 or more.

<2> The lubricating agent according to <1>, wherein the ionic liquid isrepresented by the following General Formula (1):

wherein at least one of R₁, R₂, R₃, and R₄ is a hydrogen atom, and atleast one of R₁, R₂, R₃, and R₄ is a group which contains the linearhydrocarbon group having 10 or more carbon atoms.

<3> The lubricating agent according to <1>, wherein the Bronsted base isa cyclic amidine which contains the linear hydrocarbon group having 10or more carbon atoms.<4> The lubricating agent according to <3>, wherein the ionic liquid isrepresented by the following General Formula (2):

wherein R₁₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom in a bicyclo ring.

<5> The lubricating agent according to any one of <1> to <4>, whereinthe Bronsted acid is sulfonic acid.<6> The lubricating agent according to any one of <1> to <5>, whereinthe ionic liquid has an exothermic peak temperature determined by adifferential thermal analysis (DTA) measurement of 370° C. or higher.<7> The lubricating agent according to any one of <1> to <6>, whereinthe hydrocarbon group is an alkyl group.<8> A lubricating agent, including:

an ionic liquid formed from a Bronsted acid (HX) and a Bronsted base(B),

wherein the Bronsted base has a linear hydrocarbon group having 10 ormore carbon atoms, and

wherein a difference between a pKa value of the Bronsted acid inacetonitrile and a pKa value of the Bronsted base in acetonitrile is 6or more.

<9> The lubricating agent according to <8>, wherein the ionic liquid isrepresented by the following General Formula (1):

wherein at least one of R₁, R₂, R₃, and R₄ is a hydrogen atom, and atleast one of R₁, R₂, R₃, and R₄ is a group which contains the linearhydrocarbon group having 10 or more carbon atoms.

<10> The lubricating agent according to <8>, wherein the Bronsted baseis a cyclic amidine which contains the linear hydrocarbon group having10 or more carbon atoms or a cyclic guanidine which contains the linearhydrocarbon group having 10 or more carbon atoms.<11> The lubricating agent according to <10>, wherein the ionic liquidis represented by the following General Formula (2) or (3):

wherein R₁₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom in a bicyclo ring,

wherein R₂₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom or a nitrogen atom in abicyclo ring.

<12> The lubricating agent according to any one of <8> to <11>, whereinthe ionic liquid has an exothermic peak temperature determined by adifferential thermal analysis (DTA) measurement of 370° C. or higher.<13> The lubricating agent according to any one of <8> to <12>, whereinthe Bronsted acid is perfluoroalkyl sulfonic acid, a compoundrepresented by the following Structural Formula (A), a compoundrepresented by the following Structural Formula (B), a compoundrepresented by the following Structural Formula (C), or a compoundrepresented by the following Structural Formula (D):

<14> A magnetic recording medium, including:

a non-magnetic support; and

at least a magnetic layer on or above the non-magnetic support,

wherein the magnetic layer contains the lubricating agent according toany one of <1> to <13>.

<15> An ionic liquid,

wherein the ionic liquid is formed from a Bronsted acid (HX) and aBronsted base (B),

wherein the Bronsted base has a linear hydrocarbon group having 10 ormore carbon atoms, and

wherein a difference between a pKa value of the Bronsted acid in waterand a pKa value of the Bronsted base in water is 12 or more.

<16> The ionic liquid according to <15>, wherein the ionic liquid isrepresented by the following General Formula (1):

wherein at least one of R₁, R₂, R₃, and R₄ is a hydrogen atom, and atleast one of R₁, R₂, R₃, and R₄ is a group which contains the linearhydrocarbon group having 10 or more carbon atoms.

<17> The ionic liquid according to <15>, wherein the Bronsted base is acyclic amidine which contains the linear hydrocarbon group having 10 ormore carbon atoms.<18> The ionic liquid according to <17>, wherein the ionic liquid isrepresented by the following General Formula (2):

wherein R₁₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom in a bicyclo ring.

<19> The ionic liquid according to any one of <15> to <18>, wherein theBronsted acid is sulfonic acid.<20> The ionic liquid according to any one of <15> to <19>, wherein theionic liquid has an exothermic peak temperature determined by adifferential thermal analysis (DTA) measurement of 370° C. or higher.<21> The ionic liquid according to any one of <15> to <20>, wherein thehydrocarbon group is an alkyl group.<22> The ionic liquid according to any one of <15> to <21>, wherein theBronsted base is octadecylamine (C₁₈H₃₇NH₂), decylamine (C₁₀H₂₁NH₂),tetradecylamine (C₁₄H₂₉NH₂), eicosylamine (C₂₀H₄₁NH₂), oleylamine(C₁₈H₃₅NH₂), 2-heptylundecylamine (CH₃(CH₂)_(n)CH(C₇H₁₅)NH₂), or acompound represented by the following Structural Formula (1):

<23> An ionic liquid,

wherein the ionic liquid is formed from a Bronsted acid (HX) and aBronsted base (B),

wherein the Bronsted base has a linear hydrocarbon group having 10 ormore carbon atoms, and

wherein a difference between a pKa value of the Bronsted acid inacetonitrile and a pKa value of the Bronsted base in acetonitrile is 6or more.

<24> The ionic liquid according to <23>, wherein the ionic liquid isrepresented by the following General Formula (1):

wherein at least one of R₁, R₂, R₃, and R₄ is a hydrogen atom, and atleast one of R₁, R₂, R₃, and R₄ is a group which contains the linearhydrocarbon group having 10 or more carbon atoms.

<25> The ionic liquid according to <23>, wherein the Bronsted base is acyclic amidine which contains a linear hydrocarbon group having 10 ormore carbon atoms or a cyclic guanidine which contains the linearhydrocarbon group having 10 or more carbon atoms.<26> The ionic liquid according to <25>, wherein the ionic liquid isrepresented by the following General Formula (2) or (3):

wherein R₁₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom in a bicyclo ring,

wherein R₂₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom or a nitrogen atom in abicyclo ring.

<27> The ionic liquid according to any one of <23> to <26>, wherein theionic liquid has an exothermic peak temperature determined by adifferential thermal analysis (DTA) measurement of 370° C. or higher.<28> The ionic liquid according to any one of <23> to <27>, wherein theBronsted acid is perfluoroalkyl sulfonic acid, a compound represented bythe following Structural Formula (A), a compound represented by thefollowing Structural Formula (B), a compound represented by thefollowing Structural Formula (C), or a compound represented by thefollowing Structural Formula (D):

<29> The ionic liquid according to any one of <23> to <28>, wherein theBronsted base is octadecylamine (C₁₈H₃₇NH₂), decylamine (C₁₀H₂₁NH₂),tetradecylamine (C₁₄H₂₉NH₂), eicosylamine (C₂₀H₄₁NH₂), oleylamine(C₁₈H₃₅NH₂), 2-heptylundecylamine (CH₃(CH₂)_(n)CH(C₇H₁₅)NH₂), a compoundrepresented by the following Structural Formula (2), or a compoundrepresented by the following Structural Formula (3):

Advantageous Effects of the Invention

The present invention can improve a lubricating agent in thermalstability against, for example, evaporation and thermal decomposition,and can maintain an excellent lubricating property for a long period oftime. Also, when the lubricating agent is used in a magnetic recordingmedium, the present invention can achieve the lubricating agent havingthe excellent lubricating property and an improved practicalcharacteristic such as runnability, wear resistance, and durability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating one exemplary hard diskaccording to one embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating one exemplary magnetictape according to one embodiment of the present invention.

FIG. 3 is a schematic view illustrating heat assisted magneticrecording.

FIG. 4 is a graph showing TG measurement results in Examples.

FIG. 5 shows a FTIR spectrum of the product of Example 36.

FIG. 6 shows a TG/DTA measurement result of the product of Example 36.

FIG. 7 shows a FTIR spectrum of the product of Example 37.

FIG. 8 shows a TG/DTA measurement result of the product of Example 37.

FIG. 9 shows a FTIR spectrum of the product of Example 38.

FIG. 10 shows a TG/DTA measurement result of the product of Example 38.

FIG. 11 shows a FTIR spectrum of the product of Example 39.

FIG. 12 shows a TG/DTA measurement result of the product of Example 39.

FIG. 13 shows a FTIR spectrum of the product of Example 40.

FIG. 14 shows a TG/DTA measurement result of the product of Example 40.

FIG. 15 shows a FTIR spectrum of the product of Example 41.

FIG. 16 shows a TG/DTA measurement result of the product of Example 41.

FIG. 17 shows a FTIR spectrum of the product of Example 42.

FIG. 18 shows a TG/DTA measurement result of the product of Example 42.

FIG. 19 shows a FTIR spectrum of the product of Comparative Example 27.

FIG. 20 shows a TG/DTA measurement result of the product of ComparativeExample 27.

FIG. 21 shows a FTIR spectrum of the product of Comparative Example 28.

FIG. 22 shows a TG/DTA measurement result of the product of ComparativeExample 28.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to figures in the following order.

1. Lubricating agent and ionic liquid2. Magnetic recording medium

3. Examples 1. Lubricating Agent and Ionic Liquid

A lubricating agent given as one embodiment of the present inventioncontains an ionic liquid represented by the general formula X⁻B⁺, anduses, as a Bronsted base (B), a compound containing a linear hydrocarbongroup preferably having 10 or more carbon atoms (e.g., ammonium salt).

An ionic liquid in embodiments of the present invention is a proticionic liquid synthesized through neutralization between a Bronsted acid(HX) and a Bronsted base (B).

This ionic liquid can exert an excellent thermal stability resultingfrom a difference between a pKa value of the Bronsted acid in water anda pKa value of the Bronsted base in water (ΔpKa: pKa value of Bronstedbase minus pKa value of Bronsted acid) of 12 or more.

The ionic liquid can also exert an excellent thermal stability resultingfrom a difference between a pKa value of the Bronsted acid inacetonitrile and a pKa value of the Bronsted base in acetonitrile (ΔpKa:pKa value of Bronsted base minus pKa value of Bronsted acid) of 6 ormore. Note that, the pKa values in acetonitrile is described in, forexample, Blackwell Scientific Publications, Oxford, 1990, and J. Org.Chem. 2011, Vol. 76, pp. 391-395.

Watanabe et al. have reported that proton transferability and thermalstability of a protic ionic liquid greatly depend on ΔpKa, and,therefore, when DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) is used as abase, the ionic liquid is greatly improved in the thermal stability byusing an acid having a pKa value so as to give the ΔpKa of 15 or more(Miran, M. S., Kinoshita, H., Yasuda, T., Susan, M. A. B. H., Watanabe,M., Physicochemical Properties Determined by ΔpKa for Protic IonicLiquids Based on an Organic Super-strong Base with Various BronstedAcids, Phys. Chem. Chem. Phys., Vol 14, pp. 5178-5186 (2012)).

However, it has not been sufficiently discussed what level of ΔpKa isrequired for a certain application.

The present inventors conducted extensive studies and have found thatthermal stability mechanisms are different depending on the numericalvalues of ΔpKa. It has been confirmed by TG/DTA analysis that, in thecase of small ΔpKa, weight loss of the ionic liquid is endothermic anddue to evaporation, while, in the case of large ΔpKa, weight loss of theionic liquid is exothermic and predominantly due to thermaldecomposition.

Accordingly, the present inventors found that an ionic liquid having adifference between a pKa value of a Bronsted acid in water and a pKavalue of a Bronsted base in water (ΔpKa: pKa value of Bronsted baseminus pKa value of Bronsted acid) of 12 or more exerts an excellentthermal stability and is useful as a lubricating agent.

The present inventors also found that an ionic liquid having adifference between a pKa value of a Bronsted acid in acetonitrile and apKa value of a Bronsted base in acetonitrile (ΔpKa: pKa value ofBronsted base minus pKa value of Bronsted acid) of 6 or more exerts anexcellent thermal stability and is useful as a lubricating agent.

As used herein, pKa refers to an acid dissociation constant, i.e., anacid dissociation constant in water or an acid dissociation constant inacetonitrile.

The acid dissociation constant in water can be measured, for example,with reference to the method described in J. Chem. Res., Synop. 1994,212-213. Specifically, it can be measured by a combination of aspectrometer with potentiometry.

Although the acid dissociation constant in acetonitrile is not describedherein because it is described in J. Org. Chem. 1998, 63, p. 7868 or J.Org. Chem. 1997, 62, p. 8479, it can be obtained by dissolving an acidin acetonitrile, titrating the resultant with a base, and measuring aspectrum by means of a UV-vis spectrometer.

The ionic liquid has an excellent solubility in a highly volatilesolvent such as lower alcohols (alcohols containing 1 to 3 carbon atoms)and ethers. Therefore, the ionic liquid can be easily formed into asolution when it is used. Also, the solvent can be easily removed whenthe solution is applied and used.

A compound of the present invention has a long chain alkyl group.Therefore, it has a relatively high melting point, can be producedthrough recrystallization, and can be very easily produced.

An exothermic peak temperature of the ionic liquid determined by adifferential thermal analysis (DTA) measurement is not particularlylimited and may be appropriately selected depending on the intendedpurpose, but is preferably 370° C. or higher, more preferably 400° C. to500° C. from the viewpoint of exerting excellent thermal stability.

The differential thermal analysis can be performed, for example, asfollows.

The measurement is performed in a temperature range of 30° C. to 600° C.at a heating rate of 10° C./min while introducing air at a flow rate of200 mL/min using EXSTAR 6000 (manufactured by Seiko Instruments Inc.).As a gas chromatography mass spectrometer, 6890/5975 MSD (manufacturedby Agilent Technologies, Inc.) was used. The following measurementconditions are used: column: DB-1 (15 m, diameter: 0.25 mm, membranethickness: 0.1 μm); injection temperature: 280° C.; column temperature:initial temperature of 40° C., hold for 5 min, heated to 340° C. at theheating rate of 20° C./min, and hold at the same temperature; massspectrometric unit: 5975MSD; MS detection mode: EI⁺; quadrupoletemperature: 150° C.; ion source temperature: 300° C.; mass scanningrange: m/z 33-700; and calibration: PFTBA.

The upper limit of the ΔpKa in water is not particularly limited and maybe appropriately selected depending on the intended purpose, but theΔpKa in water is preferably 25 or less, more preferably 21 or less.

The upper limit of the ΔpKa in acetonitrile is not particularly limitedand may be appropriately selected depending on the intended purpose, butthe ΔpKa in acetonitrile is preferably 40 or less, more preferably 35 orless.

The Bronsted acid satisfying the following condition is used: thedifference between the pKa value of the Bronsted acid (HX) in water andthe pKa value of the Bronsted base (B) in water is 12 or more.

Also, the Bronsted acid satisfying the following condition is used: thedifference between the pKa value of the Bronsted acid (HX) inacetonitrile and the pKa value of the Bronsted base (B) in acetonitrileis 6 or more.

Such Bronsted acid may be a super acid described in J. Org. Chem. 2005,Vol. 70, p. 1019. Preferably, Bronsted acids (HX) having a small pKa areused such as sulfonylimides (e.g., bis((trifluoromethyl)sulfonyl)imide((CF₃SO₂)₂NH), bis(nonafluorobutylsulfonyl)imide, andcyclo-hexafluoropropane-1,3-bis(sulfonyl)) and sulfonic acids (e.g.,trifluoromethane sulfonic acid (CF₃SO₃H), sulfuric acid (H₂SO₄), methanesulfonic acid (CH₃SO₃H), and perfluorooctane sulfonic acid (C₈F₁₇SO₃H)).

In addition, the Bronsted acid may be perfluoroalkyl sulfonic acid, acompound represented by the following Structural Formula (A), a compoundrepresented by the following Structural Formula (B), a compoundrepresented by the following Structural Formula (C), or a compoundrepresented by the following Structural Formula (D):

The Bronsted acid may also be organic acids described in Table 1 in thefollowing non-patent literature: Agnes Kutt, Toomas Rodima, Jaan Saame,Elin Raamat, Vahur Maemets, Ivari Kaljurand, Ilmar A. Koppel, Romute Yu.Garlyauskayte, Yurii L. Yagupolskii, Lev M. Yagupolskii, EduardBernhardt, Helge Willner, and Ivo Leito, “Equilibrium Acidities ofSuperacids”, J. Org. Chem. 2011, Vol. 76, pp. 391-395.

The pKa of the Bronsted acid in water is not particularly limited andmay be appropriately selected depending on the intended purpose, but ispreferably −18 to −3.

The pKa of the Bronsted acid in acetonitrile is not particularly limitedand may be appropriately selected depending on the intended purpose, butis preferably −5 to −12.

An organic base compound satisfying the condition that the differencebetween the pKa value of the Bronsted acid (HX) in water and the pKavalue of the Bronsted base (B) in water (ΔpKa) is 12 or more andcontaining a linear hydrocarbon group preferably having 10 or morecarbon atoms (e.g., ammonium salt) may be used as the Bronsted base. Thelong hydrocarbon chain thereof enables a reduced coefficient of frictionand an improved lubricating property.

An organic base compound satisfying the condition that the differencebetween the pKa value of the Bronsted acid (HX) in acetonitrile and thepKa value of the Bronsted base (B) in acetonitrile (ΔpKa) is 6 or moreand containing a linear hydrocarbon group preferably having 10 or morecarbon atoms (e.g., ammonium salt) may be used as the Bronsted base. Thelong hydrocarbon chain thereof enables a reduced coefficient of frictionand an improved lubricating property.

The organic base compound is preferably a compound having a high pKa.

Examples of the organic base compound includes amines, hydroxyamines,imines, oximes, hydrazines, hydrazones, guanidine, amidines, sulfoamide,imides, amides, thioamides, carbamates, nitriles, ureas, urethanes, andcyclic heterocycles. Examples of the cyclic heterocycles includepyrrole, indole, azole, oxazole, triazole, tetrazole, and imidazole.

The Bronsted acid may also be organic bases described in Table 1 in thefollowing non-patent literature: Ivari Kaljurand, Agnes Kuett, LilliSoovaeli, Toomas Rodima, Vahur Maeemets, Ivo Leito, and Ilmar A. Koppel,“Extension of the Self-Consistent Spectrophotometric Basicity Scale inAcetonitrile to a Full Span of 28 pKa Units: Unification of DifferentBasicity Scales” J. Org. Chem. 2005, Vol. 70, pp. 1019-1028.

The upper limit of the number of carbon atoms in the linear hydrocarbongroup having 10 or more carbon atoms is not particularly limited and maybe appropriately selected depending on the intended purpose. However,the number of carbon atoms is preferably 25 or less, more preferably 20or less from the viewpoint of raw material procurement.

The hydrocarbon group may be a saturated hydrocarbon group, anunsaturated hydrocarbon group having a double bond, or an unsaturatedbranched hydrocarbon group having a branch, as long as it is linear.Among them, the hydrocarbon group is preferably an alkyl group which isthe saturated hydrocarbon group from the viewpoint of wear resistance. Alinear hydrocarbon group having no branch is also preferable.

The pKa value of the Bronsted base in water is not particularly limitedand may be appropriately selected depending on the intended purpose, butis preferably 9 to 30.

The pKa value of the Bronsted base in acetonitrile is not particularlylimited and may be appropriately selected depending on the intendedpurpose, but is preferably 15 to 35.

Example of the Bronsted base includes a compound containing a nitrogenwhich is positively charged when it forms an ion pair with the Bronstedacid. Examples of such compound include amines, hydroxylamines, imines,oximes, hydrazines, hydrazones, guanidine, amidines, sulfoamide, imides,amides, thioamides, carbamates, nitriles, ureas, urethanes, and cyclicheterocycles. Examples of the cyclic heterocycles include pyrrole,indole, azole, oxazole, triazole, tetrazole, and imidazole, as well asthe aliphatic amine, an aromatic amine, a cyclic amine, and amidine.Examples of the aliphatic amine includes a primary aliphatic amine, asecondary aliphatic amine, and a tertiary aliphatic amine. Examples ofthe aromatic amine includes aniline, diphenylamine, and 4-aminopyridine.Examples of the cyclic amine includes pyrrolidone,2,2,6,6-tetramethylpiperidine, and quinuclidine. Examples of the amidineincludes a cyclic amidine.

Specific examples of preferable Bronsted base include aliphatic aminessuch as octadecylamine (C₁₈H₃₇NH₂), decylamine (C₁₀H₂₁NH₂),tetradecylamine (C₁₄H₂₉NH₂), eicosylamine (C₂₀H₄₁NH₂), oleylamine(C₁₈H₃₅NH₂), and 2-heptylundecylamine (CH₃(CH₂)_(n)CH(C₇H₁₅)NH₂). It isneedless to say that the structure of the amines are not limitedthereto. For example, the amines may be those in which a hydrocarbonchain is introduced into a heterocyclic compound, an alicyclic compound,or an aromatic compound. Additionally, a compound represented by thefollowing Structural Formula (1), a compound represented by thefollowing Structural Formula (2), and a compound represented by thefollowing Structural Formula (3) are also preferably used.

An ionic liquid containing the aliphatic amine as the Bronsted base isrepresented by the following General Formula (1):

In General Formula (1), at least of R₁, R₂, R₃, and R₄ is a hydrogenatom, and at least one of R₁, R₂, R₃, and R₄ is a group which contains alinear hydrocarbon group having 10 or more carbon atoms. R group otherthan the linear hydrocarbon group having 10 or more carbon atoms ispreferably a branched hydrocarbon, an aromatic ring, an alicycle, ahydrocarbon having an unsaturated bond, or hydrogen. Alternatively, theR group may be a heterocyclic compound or those having a substitutedhalogen.

The group which contains a linear hydrocarbon group having 10 or morecarbon atoms is preferably a linear hydrocarbon group having 10 or morecarbon atoms.

The ionic liquid is preferably one in which the Bronsted base is acyclic amidine which contains a linear hydrocarbon group having 10 ormore carbon atoms or a cyclic guanidine which contains a linearhydrocarbon group having 10 or more carbon atoms. Examples of the cyclicamidine include imidazole, benzimidazole,1,8-diazabicyclo(5,4,0)-undecene-7 (DBU), and1,5-diazabicyclo(4,3,0)-nonene-5 (DBN). Note that, the pKa value ofimidazole is 14, the pKa value of DBU in water is 12.5, and the pKavalue of DBN in water is 12.7. Examples of the cyclic guanidine include1,5,7-triazabicyclo[4.4.0]-5-decene (TBD). A compound referred to as asuper base described in Chem. Eur. J. 2012, Vol. 18, p. 3621 or J. Org.Chem. 2005, Vol. 70, p. 1019 may be used as the Bronsted base.

The ionic liquid is preferably a compound represented by the followingGeneral Formula (2), more preferably a compound represented by thefollowing General Formula (2-1).

The ionic liquid is preferably a compound represented by the followingGeneral Formula (3), more preferably a compound represented by thefollowing General Formula (3-1).

In the General Formula (2), R₁₁ denotes a linear hydrocarbon grouphaving 10 or more carbon atoms and being attached to a carbon atom in abicyclo ring.

In the General Formula (2-1), R₁₁ denotes a linear hydrocarbon grouphaving 10 or more carbon atoms.

In the General Formula (3), R₂₁ denotes a linear hydrocarbon grouphaving 10 or more carbon atoms and being attached to a carbon atom or anitrogen atom in a bicyclo ring.

In the General Formula (3-1), R₂₁ denotes a linear hydrocarbon grouphaving 10 or more carbon atoms.

Hereinafter, one exemplary synthetic method of the ionic liquid will bedescribed. The ionic liquid is synthesized from the Bronsted acid andthe Bronsted base. Specifically, the ionic liquid is obtained by mixing,for example, sulfonic acid with an equal amount of an organic basecompound to neutralize them.

Alternatively, the ionic liquid can be obtained by neutralizing analiphatic amine with nitric acid to produce an ammonium nitrate salt,followed by anion exchange. For example, the ionic liquid can beobtained by anion exchange of ammonium nitrate salt with an equal amountof bis(trifluoromethanesulfonyl)amide lithium salt (Li[(CF₃SO₂)₂N]), asrepresented by the following Reaction Scheme (2).

The lubricating agent in the present embodiment may contain theaforementioned ionic liquid alone or in combination with conventionallyknown lubricating agents. For example, the ionic liquid may be combinedwith a long chain carboxylic acid, a long chain carboxylic acid ester,perfluoroalkyl carboxylic acid ester, carboxylic acid perfluoroalkylester, perfluoroalkyl carboxylic acid perfluoroalkyl ester, or aperfluoropolyether derivative.

In order to keep a lubricating effect under a harsh condition, anextreme pressure agent may be used in combination in a compounding ratioof 30:70 to 70:30 by mass. When partial metal-to-metal contact occurs ina boundary-lubrication area, the extreme pressure agent reacts with ametal surface by the action of frictional heat generated accompanyingthe contact to thereby form a reaction product film. Thus, the extremepressure agent exerts an abrasion and wear prevention effect. Theextreme pressure agent may be any of, for example, a phosphorus-basedextreme pressure agent, a sulfur-based extreme pressure agent, ahalogen-based extreme pressure agent, an organic metal-based extremepressure agent, and a complex type extreme pressure agent.

An anti-rust agent may be used in combination, if necessary. Theanti-rust agent may be those being commonly available as an anti-rustagent for this type of magnetic recording medium. Examples thereofinclude phenols, naphthols, quinones, a nitrogen-containing heterocycliccompound, an oxygen-containing heterocyclic compound, and asulfur-containing heterocyclic compound. The anti-rust agent may bemixed with the lubricating agent. Alternatively, the anti-rust agent andthe lubricating agent may be deposited separately in two or more layerby, for example, forming a magnetic layer on a non-magnetic support,applying an anti-rust agent layer thereon, followed by applying alubricating agent layer thereon.

A solvent for the lubricating agent may be alcohol-based solvents suchas isopropyl alcohol (IPA) and ethanol, which may be used alone or incombination. For example, hydrocarbon-based solvents such as n-hexane orfluorosolvents may be used in combination therewith.

2. Magnetic Recording Medium

Next, a magnetic recording medium containing the aforementionedlubricating agent will now be described. A magnetic recording mediumgiven as one embodiment of the present invention includes a non-magneticsupport and a magnetic layer thereon, and the magnetic layer containsthe aforementioned lubricating agent.

The lubricating agent in the present embodiment can be applied to amagnetic recording medium formed by depositing the magnetic layer on asurface of the non-magnetic support by a technique such as vapordeposition and sputtering, which is the so-called metallic thin filmtype magnetic recording medium. Additionally, the lubricating agent canbe applied to a magnetic recording medium having a configuration inwhich an under layer is interposed between the non-magnetic support andthe magnetic layer. Examples of such magnetic recording medium include amagnetic disk and a magnetic tape.

FIG. 1 is a cross-sectional view illustrating one exemplary hard disk.This hard disk has a configuration in which a substrate 11, an underlayer 12, a magnetic layer 13, a carbon protecting layer 14, and alubricating agent layer 15 are sequentially laminated.

FIG. 2 is a cross-sectional view illustrating one exemplary magnetictape. This magnetic tape has a configuration in which a back coat layer25, a substrate 21, a magnetic layer 22, a carbon protecting layer 23,and a lubricating agent layer 24 are sequentially laminated.

In the magnetic disk illustrated in FIG. 1, the non-magnetic supportcorresponds to the substrate 11 and the under layer 12. In the magnetictape illustrated in FIG. 2, the non-magnetic support corresponds to thesubstrate 21. In the case where a rigid substrate such as an Al alloyplate and a glass plate is used as the non-magnetic support, a surfaceof the substrate may be made hard by forming an oxide film (for example,through an alumite treatment) or a Ni—P film thereon.

The magnetic layers 13 and 22 are formed as continuous films by atechnique such as plating, sputtering, vacuum deposition, and plasmaCVD. Examples of the magnetic layers 13 and 22 include an in-planemagnetization recording metallic magnetic film consisting of, forexample, a metal (e.g., Fe, Co, or Ni), a Co—Ni based alloy, a Co—Ptbased alloy, a Co—Ni—Pt based alloy, a Fe—Co based alloy, a Fe—Ni basedalloy, a Fe—Co—Ni based alloy, a Fe—Ni—B based alloy, a Fe—Co—B basedalloy, and a Fe—Co—Ni—B based alloy; and a perpendicular magnetizationrecording metallic magnetic film such as a Co—Cr based alloy film and aCo—O based film.

In particular, in the case where the in-plane magnetization recordingmetallic magnetic film is formed, orientation may be eliminated, planarisotropy may be ensured, and coercive force may be improved as follows.A non-magnetic material (e.g., Bi, Sb, Pb, Sn, Ga, In, Ge, Si, and Tl)is formed as the under layer 12 on the non-magnetic support in advance,and a metallic magnetic material is vertically vapor-deposited orsputtered thereon to thereby disperse the non-magnetic material into themagnetic metallic thin film.

Hard protecting layers 14 and 23 (e.g., a carbon film, a diamond-likecarbon film, a chromium oxide film, or SiO₂ film) may be formed onsurfaces of the magnetic layers 13 and 22.

Example of a method for allowing the aforementioned lubricating agent tobe contained in such metallic thin film type magnetic recording mediumincludes a method in which the lubricating agent is applied, as a topcoat, onto surfaces of the magnetic layers 13 and 22 or surfaces of theprotecting layers 14 and 23, as illustrated in FIGS. 1 and 2. An amountof the lubricating agent to be applied is preferably 0.1 mg/m²˜100mg/m², more preferably 0.5 m g/m²˜30 mg/m², particularly preferably 0.5mg/m²˜20 mg/m².

As illustrated in FIG. 2, the metallic thin film type magnetic tape maycontain a back coat layer 25, if necessary, in addition to the magneticlayer 22 serving as the metallic magnetic thin film.

The back coat layer 25 is formed by adding carbon-based powder forimparting electroconductivity and an inorganic pigment for controllingsurface roughness to a resin binder, followed by applying. In thepresent embodiment, the aforementioned lubricating agent may beinternally added or contained as the top coat in the back coat layer 25.Alternatively, the aforementioned lubricating agent may be internallyadded or contained as the top coat in the magnetic layer 22 and the backcoat layer 25.

In another embodiment, the lubricating agent can be applied to amagnetic recording medium in which magnetic paint is applied onto asurface of the non-magnetic support to thereby form a magnetic coatingfilm serving as the magnetic layer, which is the so-called coating typemagnetic recording medium. In the coating type magnetic recordingmedium, any conventionally known resin binder and magnetic powderconstituting the non-magnetic support or the magnetic coating film canbe used.

Examples of the non-magnetic support include a polymeric support formedof, for example, a polymeric material such as polyesters, polyolefins,cellulose derivatives, vinyl-based resins, polyimides, polyamides, andpolycarbonates; a metallic substrate formed of, for example, aluminiumalloy or titanium alloy; a ceramic substrate formed of, for example,alumina glass; and a glass substrate. The shape thereof is notparticularly limited, and may be any shape such as a tape-like shape, asheet-like shape, or a drum-like shape. In addition, the non-magneticsupport may be surface-treated to form fine unevenness in order tocontrol its surface nature.

Examples of the magnetic powder include ferromagnetic iron oxide-basedparticles (e.g., γ-Fe₂O₃ and cobalt-coated γ-Fe₂O₃), ferromagneticchromium dioxide-based particles, ferromagnetic metal-based particlesconsisting of a metal (e.g., Fe, Co, and Ni) or alloy containing it, andhexagonal crystal-based ferrite particles having a hexagonal-plate-likeshape.

Examples of the resin binder include a polymer such as vinyl chloride,vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic ester,methacrylic ester, styrene, butadiene, and acrylonitrile; a copolymer ofany two or more of these polymers; a polyurethane resin, a polyesterresin, and an epoxy resin. In order to improve dispersibility of themagnetic powder, a hydrophilic polar group such as a carboxylic acidgroup, a carboxyl group, or a phosphate group may be introduced into thebinder.

The magnetic coating film may contain an additive such as a dispersingagent, an abrasive agent, an antistatic agent, and an anti-rust agent,in addition to the magnetic powder and the resin binder.

Examples of a method for allowing the aforementioned lubricating agentto be contained in such coating type magnetic recording medium includesa method in which the lubricating agent is internally added to themagnetic layer constituting the magnetic coating film formed on thenon-magnetic support, a method in which the lubricating agent isdeposited onto a surface of the magnetic layer as the top coat, and acombination thereof. In the case where the lubricating agent isinternally added to the magnetic coating film, the lubricating agent isadded in the amount of 0.2 parts by mass to 20 parts by mass relative to100 parts by mass of the resin binder.

In the case where the lubricating agent is deposited onto a surface ofthe magnetic layer as the top coat, the lubricating agent is preferablyapplied in the amount of 0.1 mg/m² to 100 mg/m², more preferably 0.5 mg/m² to 20 mg/m². Note that, a method for depositing the lubricatingagent as the top coat may be a method in which the ionic liquid isdissolved in a solvent, and then the resultant solution is applied orsprayed, or a magnetic recording medium is immersed into the solution.

In the present embodiment, a lubricating agent containing an ionicliquid which is formed from a Bronsted acid and a Bronsted basecontaining a linear hydrocarbon group preferably having 10 or morecarbon atoms and which has a difference of pKa values thereof (ΔpKa) inwater is 12 or more can exert a good lubricating effect to therebyreduce a coefficient of friction and achieve thermally high stability.The lubricating effect is not impaired even under a harsh condition suchas high temperature, low temperature, high humidity, or low humidity.

In the present embodiment, a lubricating agent containing an ionicliquid which is formed from a Bronsted acid and a Bronsted basecontaining a linear hydrocarbon group preferably having 10 or morecarbon atoms and which has a difference of pKa values thereof (ΔpKa) inacetonitrile is 6 or more can exert a good lubricating effect to therebyreduce a coefficient of friction and achieve thermally high stability.The lubricating effect is not impaired even under a harsh condition suchas high temperature, low temperature, high humidity, or low humidity.

Thus, the magnetic recording medium to which the lubricating agent inthe present embodiment is applied can exert excellent runnability, wearresistance, and durability and can improve thermal stability due to itslubricating effect.

EXAMPLES 3. Example

Hereinafter, specific examples of the present invention will now bedescribed. In Examples, ionic liquids were synthesized, and lubricationagents containing the ionic liquids were produced. Then, magnetic disksand magnetic tapes were produced using the lubrication agents, each ofwhich was evaluated for disk durability and tape durability. Productionof the magnetic disks, a disk durability test, production of themagnetic tapes, and a tape durability test were performed as follows.Note that, the present invention is not limited to Examples.

<Production of Magnetic Disk>

A magnetic disk illustrated in FIG. 1 was produced by forming a magneticthin film on a glass substrate according to, for example, InternationalPublication No. WO2005/068589. Specifically, a chemically strengthenedglass disk consisting of aluminosilicate glass (external diameter: 65mm, internal diameter: 20 mm, disk thickness: 0.635 mm) was prepared. Asurface of the disk was polished so as to have Rmax of 4.8 nm and Ra of0.43 nm. The glass substrate was subjected to ultrasonic cleaning inpure water and isopropyl alcohol (IPA) (purity: 99.9% or higher) for 5min each, and then left to stand in IPA saturated vapor for 1.5 min,followed by drying, which was determined as a substrate 11.

On this substrate 11, 30 nm of a NiAl alloy (Ni: 50 mol %, Al: 50 mol %)thin film serving as a seed layer, 8 nm of a CrMo alloy (Cr: 80 mol %,Mo: 20 mol %) thin film serving as a under layer 12, and 15 nm of aCoCrPtB alloy (Co: 62 mol %, Cr: 20 mol %, Pt: 12 mol %, and B: 6 mol %)serving as a magnetic layer 13 were sequentially formed by a DCmagnetron sputtering method.

Next, a 5 nm of carbon protecting layer 14 consisting of amorphousdiamond-like carbon was formed by a plasma CVD method. The thus formeddisk sample was subjected to ultrasonic cleaning in isopropyl alcohol(IPA) (purity: 99.9% or higher) contained in a cleaning vessel for 10min to thereby remove contaminants on a surface of the disk, followed bydrying. Then, a solution of an ionic liquid in IPA was applied onto thesurface of the disk by a dip coating method under an environment of 25°C. and 50% relative humidity (RH) to thereby form an about 1 nm of alubricating agent layer 15.

<Disk Durability Test>

A CSS durability test was performed using a commercially availablestrain gauge type disk friction and wear tester as follows. A hard diskwas mounted on a rotary spindle with tightening torque of 14.7 Ncm, andthen, a head slider was mounted on the hard disk so that the center ofan air bearing surface of the head slider in an inner peripheral sidewas 17.5 mm apart from the center of the hard disk. The head used inthis measurement was IBM 3370 type in-line head, the slider was made ofAl₂O₃—TiC, and a head load was 63.7 mN. In this test, the maximum valueof friction force was monitored every CSS (Contact, Start, Stop) underan environment of 25° C., 60% RH, and cleanliness of 100. The number oftimes in which a coefficient of friction exceeds 1.0 was determined as aresult of the CSS durability test. In the result of the CSS durabilitytest, when the number of times was greater than 50,000, the result wasdisplayed as “>50,000.” To examine thermal resistance, the CSSdurability test was performed again in the same manner after a heatingtest at a temperature of 300° C. for 3 min.

<Production of Magnetic Tape>

A magnetic tape having a cross-sectional configuration as shown in FIG.2 was produced. Firstly, Co was deposited onto a substrate 21 consistingof a MICTRON (aromatic polyamide) film having a thickness of 5 μm(manufactured by Toray Industries, Inc.) by an oblique deposition methodto thereby form a magnetic layer 22 consisting of a 100 nm thickferromagnetic metal thin film. Next, a 10 nm of carbon protecting layer23 consisting of carbon-like carbon was formed on a surface of theferromagnetic metal thin film by the plasma CVD method, followed bycutting to 6 mm width. The ionic liquid dissolved in IPA was appliedonto the magnetic layer 22 so as to have a film thickness of about 1 nmto thereby form a lubricating agent layer 24. Thus, a sample tape wasproduced.

<Tape Durability Test>

For each sample tape, still durability under an environment of atemperature of −5° C. and an environment of a temperature of 40° C. and30% RH, and a coefficient of friction and shuttle durability under anenvironment of a temperature of −5° C. and an environment of atemperature of 40° C. and 90% RH were measured. The still durability wasevaluated as attenuation time for which the output in the pause statewas decreased by −3 dB. The shuttle durability was evaluated as thenumber of shuttle runs before the output was decreased by 3 dB when thesample tape was subjected to repeated shuttle running operations for 2min per run. Additionally, in order to examine thermal resistance, thedurability test was performed again in the same manner after a heatingtest at a temperature of 100° C. for 10 min.

<3.1 Effect of Difference Between pKa Value of Bronsted Acid and pKaValue of Bronsted Base (ΔpKa)>

Ionic liquids were synthesized having different differences between pKavalues of Bronsted acids and pKa values of Bronsted bases (ΔpKa).Lubricating agents containing the ionic liquids were used in magneticrecording media to examine an effect of the difference between a pKavalue of a Bronsted acid and a pKa value of a Bronsted base (ΔpKa).

Note that, pKa values in Examples 1 to 35 and Comparative Examples 1 to26 refer to pKa values in water, and pKa values in Examples 36 to 56 andComparative Examples 27 to 32 refer to pKa values in acetonitrile.

Example 1 Ionic Liquid 1

As described in Table 2, bis(trifluoromethylsulfonyl)imide (pKa=−10) wasused as the Bronsted acid, and octadecylamine containing a linearhydrocarbon group having 18 carbon atoms (pKa=10.7) was used as theBronsted base. The difference between a pKa value of a Bronsted acid anda pKa value of a Bronsted base (ΔpKa) was 20.7. Ionic liquid 1 wassynthesized by neutralizing octadecylamine with nitric acid to producean ammonium nitrate salt, followed by anion exchange of the ammoniumnitrate salt with an equal amount of bis(trifluoromethylsulfonyl)imidelithium salt (Li[(CF₃SO₂)₂N]). Note that, Ionic liquid 1 was the samecompound as Ionic liquid 12 described below, and the detailed syntheticmethod thereof was as described in the synthetic method of Ionic liquid12.

Example 2 Ionic Liquid 2

As described in Table 2, trifluoromethane sulfonic acid (CF₃SO₃H,pKa=−7) was used as the Bronsted acid, and octadecylamine containing alinear hydrocarbon group having 18 carbon atoms (pKa=10.7) was used asthe Bronsted base. The difference between a pKa value of a Bronsted acidand a pKa value of a Bronsted base (ΔpKa) was 17.7. Ionic liquid 2 wassynthesized by mixing octadecylamine with an equal amount oftrifluoromethane sulfonic acid to thereby neutralize it.

Example 3 Ionic Liquid 3

As described in Table 2, sulfuric acid (H₂SO₄, pKa=−3) was used as theBronsted acid, and octadecylamine containing a linear hydrocarbon grouphaving 18 carbon atoms (pKa=10.7) was used as the Bronsted base. Thedifference between a pKa value of a Bronsted acid and a pKa value of aBronsted base (ΔpKa) was 13.7. Ionic liquid 3 was synthesized by mixingoctadecylamine with an equal amount of sulfuric acid to therebyneutralize it.

Example 4 Ionic Liquid 4

As described in Table 2, methane sulfonic acid (CH₃SO₃H, pKa=−2) wasused as the Bronsted acid, and octadecylamine containing a linearhydrocarbon group having 18 carbon atoms (pKa=10.7) was used as theBronsted base. The difference between a pKa value of a Bronsted acid anda pKa value of a Bronsted base (ΔpKa) was 12.7. Ionic liquid 4 wassynthesized by mixing octadecylamine with an equal amount oftrifluoromethane sulfonic acid to thereby neutralize it.

Comparative Example 1 Comparative Ionic Liquid 1

As described in Table 2, trifluoroacetic acid (CF₃COOH, pKa=0.5) wasused as the Bronsted acid, and octadecylamine containing a linearhydrocarbon group having 18 carbon atoms (pKa=10.7) was used as theBronsted base. The difference between a pKa value of a Bronsted acid anda pKa value of a Bronsted base (ΔpKa) was 10.2. Comparative ionic liquid1 was synthesized by mixing octadecylamine with an equal amount oftrifluoroacetic acid to thereby neutralize it.

Comparative Example 2 Comparative Ionic Liquid 2

As described in Table 2, perfluorooctanoic acid (C₇F₁₅COOH, pKa=2.5) wasused as the Bronsted acid, and octadecylamine containing a linearhydrocarbon group having 18 carbon atoms (pKa=10.7) was used as theBronsted base. The difference between a pKa value of a Bronsted acid anda pKa value of a Bronsted base (ΔpKa) was 8.2. Comparative ionic liquid2 was synthesized by mixing octadecylamine with an equal amount ofperfluorooctanoic acid to thereby neutralize it.

Comparative Example 3 Comparative Ionic Liquid 3

As described in Table 2, stearic acid (C₁₇F₃₅COOH, pKa=5.0) was used asthe Bronsted acid, and octadecylamine containing a linear hydrocarbongroup having 18 carbon atoms (pKa=10.7) was used as the Bronsted base.The difference between a pKa value of a Bronsted acid and a pKa value ofa Bronsted base (ΔpKa) was 5.7. Comparative ionic liquid 3 wassynthesized by mixing octadecylamine with an equal amount of stearicacid to thereby neutralize it.

TABLE 2 Structural Formula pKa of of Bronsted acid Bronsted acid ΔpKaIonic liquid 1

−10 20.7 Ionic liquid 2 CF₃SO₃H −7 17.7 Ionic liquid 3 H₂SO₄ −3 13.7Ionic liquid 4 CH₃SO₃H −2 12.7 Comparative CF₃COOH 0.5 10.2 ionic liquid1 Comparative C₇F₁₅COOH 2.5 8.2 ionic liquid 2 Comparative C₁₇H₃₅COOH5.0 5.7 ionic liquid 3

Example 5

A magnetic disk was produced as described above using a lubricatingagent containing Ionic liquid 1. As described in Table 3, the CSSmeasurement result of the magnetic disk was greater than 50,000, the CSSmeasurement result after the heating test was also greater than 50,000,indicating excellent durability.

Example 6

A magnetic disk was produced as described above using a lubricatingagent containing Ionic liquid 2. As described in Table 3, the CSSmeasurement result of the magnetic disk was greater than 50,000, the CSSmeasurement result after the heating test was also greater than 50,000,indicating excellent durability.

Example 7

A magnetic disk was produced as described above using a lubricatingagent containing Ionic liquid 3. As described in Table 3, the CSSmeasurement result of the magnetic disk was greater than 50,000, the CSSmeasurement result after the heating test was also greater than 50,000,indicating excellent durability.

Example 8

A magnetic disk was produced as described above using a lubricatingagent containing Ionic liquid 4. As described in Table 3, the CSSmeasurement result of the magnetic disk was greater than 50,000, the CSSmeasurement result after the heating test was also greater than 50,000,indicating excellent durability.

Comparative Example 4

A magnetic disk was produced as described above using a lubricatingagent containing Comparative ionic liquid 1. As described in Table 3,the CSS measurement result of the magnetic disk was greater than 50,000,but the CSS measurement result after the heating test was 1,230,indicating that the heating test deteriorated durability. It is believedthat this is because high temperature allowed ionic dissociation toproceed to thereby deteriorate thermal stability.

Comparative Example 5

A magnetic disk was produced as described above using a lubricatingagent containing Comparative ionic liquid 2. As described in Table 3,the CSS measurement result of the magnetic disk was greater than 50,000,but the CSS measurement result after the heating test was 891,indicating that the heating test deteriorated durability. It is believedthat this is because, as with Comparative Example 4, high temperatureallowed ionic dissociation to proceed to thereby deteriorate thermalstability.

Comparative Example 6

A magnetic disk was produced as described above using a lubricatingagent containing Comparative ionic liquid 3. As described in Table 3,the CSS measurement result of the magnetic disk was greater than 50,000,but the CSS measurement result after the heating test was 803,indicating that the heating test deteriorated durability. It is believedthat this is because, as with Comparative Example 4, high temperatureallowed ionic dissociation to proceed to thereby deteriorate thermalstability.

TABLE 3 Lubricating agent CSS durability CSS durability after heatingExample 5 Ionic liquid 1 25° C., 60% RH >50,000 25° C., 60% RH >50,000Example 6 Ionic liquid 2 25° C., 60% RH >50,000 25° C., 60% RH >50,000Example 7 Ionic liquid 3 25° C., 60% RH >50,000 25° C., 60% RH >50,000Example 8 Ionic liquid 4 25° C., 60% RH >50,000 25° C., 60% RH >50,000Comparative Comparative 25° C., 60% RH >50,000 25° C., 60% RH 1,230Example 4 ionic liquid 1 Comparative Comparative 25° C., 60% RH >50,00025° C., 60% RH 891 Example 5 ionic liquid 2 Comparative Comparative 25°C., 60% RH >50,000 25° C., 60% RH 803 Example 6 ionic liquid 3

Next, Examples in which Ionic liquids 1 to 4 and Comparative ionicliquids 1 to 3 were applied to magnetic tapes will now be described.

Example 9

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 1. As described in Table 4, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.19 under the environment of a temperature of −5° C.and 0.23 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 1 was applied hasexcellent frictional property, still durability, and shuttle durability.

Example 10

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 2. As described in Table 4, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.20 under the environment of a temperature of −5° C.and 0.23 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 2 was applied hasexcellent frictional property, still durability, and shuttle durability.

Example 11

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 3. As described in Table 4, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.25 under the environment of a temperature of −5° C.and 0.28 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 3 was applied hasexcellent frictional property, still durability, and shuttle durability.

Example 12

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 4. As described in Table 4, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.24 under the environment of a temperature of −5° C.and 0.28 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 4 was applied hasexcellent frictional property, still durability, and shuttle durability.

Comparative Example 7

A magnetic tape was produced as described above using the lubricatingagent containing Comparative ionic liquid 1. As described in Table 4,the coefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.23 under the environment of a temperature of −5° C.and 0.30 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were 45 min under theenvironment of a temperature of −5° C. and 59 min under the environmentof a temperature of 40° C. and a relative humidity of 30%. The shuttledurabilities were 135 times under the environment of a temperature of−5° C. and 126 times under the environment of a temperature of 40° C.and a relative humidity of 90%. The still durabilities after the heatingtests were 26 min under the environment of a temperature of −5° C. and31 min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests were55 times under the environment of a temperature of −5° C. and 42 timesunder the environment of a temperature of 40° C. and a relative humidityof 90%. From these results, it has been found that the magnetic tapeonto which Comparative ionic liquid 1 was applied is greatlydeteriorated in the still durability after the heating test and theshuttle durability after the heating test.

Comparative Example 8

A magnetic tape was produced as described above using the lubricatingagent containing Comparative ionic liquid 2. As described in Table 4,the coefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.21 under the environment of a temperature of −5° C.and 0.25 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were 12 min underthe environment of a temperature of −5° C. and 16 min under theenvironment of a temperature of 40° C. and a relative humidity of 30%.The shuttle durabilities after the heating tests were 30 times under theenvironment of a temperature of −5° C. and 23 times under theenvironment of a temperature of 40° C. and a relative humidity of 90%.From these results, it has been found that the magnetic tape onto whichComparative ionic liquid 2 was applied is greatly deteriorated in thestill durability after the heating test and the shuttle durability afterthe heating test.

Comparative Example 9

A magnetic tape was produced as described above using the lubricatingagent containing Comparative ionic liquid 3. As described in Table 4,the coefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.21 under the environment of a temperature of −5° C.and 0.25 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were 7 min under theenvironment of a temperature of −5° C. and 9 min under the environmentof a temperature of 40° C. and a relative humidity of 30%. The shuttledurabilities after the heating tests were 15 times under the environmentof a temperature of −5° C. and 12 times under the environment of atemperature of 40° C. and a relative humidity of 90%. From theseresults, it has been found that the magnetic tape onto which Comparativeionic liquid 3 was applied is greatly deteriorated in the stilldurability after the heating test and the shuttle durability after theheating test.

TABLE 4 Coefficient of friction after Shuttle Lubricating 100 times ofStill Shuttle Still durability durability after agent shuttle runsdurability/min durability after heating heating Ex. 9 Ionic liquid 1 −5°C.  0.19 −5° C.  >60 −5° C.  >200 −5° C.  >60 −5° C.  >200 40° C., 0.2340° C., >60 40° C., >200 40° C., >60 40° C., >200 90% RH 30% RH 90% RH30% RH 90% RH Ex. 10 Ionic liquid 2 −5° C.  0.20 −5° C.  >60 −5°C.  >200 −5° C.  >60 −5° C.  >200 40° C., 0.23 40° C., >60 40° C., >20040° C., >60 40° C., >200 90% RH 30% RH 90% RH 30% RH 90% RH Ex. 11 Ionicliquid 3 −5° C.  0.25 −5° C.  >60 −5° C.  >200 −5° C.  >60 −5° C.  >20040° C., 0.28 40° C., >60 40° C., >200 40° C., >60 40° C., >200 90% RH30% RH 90% RH 30% RH 90% RH Ex. 12 Ionic liquid 4 −5° C.  0.24 −5°C.  >60 −5° C.  >200 −5° C.  >60 −5° C.  >200 40° C., 0.28 40° C., >6040° C., >200 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 30% RH 90% RHComp. Comparative −5° C.  0.23 −5° C.    45 −5° C.    135 −5° C.    26−5° C.     55 Ex. 7 ionic liquid 1 40° C., 0.30 40° C.,   59 40° C.,  126 40° C.,   31 40° C.,    42 90% RH 30% RH 90% RH 30% RH 90% RHComp. Comparative −5° C.  0.21 −5° C.  >60 −5° C.  >200 −5° C.    12 −5°C.     30 Ex. 8 ionic liquid 2 40° C., 0.25 40° C., >60 40° C., >200 40°C.,   16 40° C.,    23 90% RH 30% RH 90% RH 30% RH 90% RH Comp.Comparative −5° C.  0.21 −5° C.  >60 −5° C.  >200 −5° C.     7 −5° C.    15 Ex. 9 ionic liquid 3 40° C., 0.25 40° C., >60 40° C., >200 40° C.,   9 40° C.,    12 90% RH 30% RH 90% RH 30% RH 90% RH

As can be seen from Tables 3 and 4, use of the ionic liquid having thedifference between the pKa value of the Bronsted acid in water and thepKa value of the Bronsted base in water (ΔpKa) of 12 or more can achieveexcellent thermal stability and durability.

<3.2 Effects of Number of Carbon Atoms and Structure in LinearHydrocarbon of Bronsted Base>

Next, ionic liquids were synthesized using, as the Bronsted base,aliphatic amines having the different number of carbon atoms andstructures (double bond, partially branched) in linear hydrocarbons.Lubricating agents containing the ionic liquids were used in magneticrecording media to examine effects of the number of carbon atoms and thestructure in the linear hydrocarbon of the Bronsted base. Note that,Bronsted basicity of the aliphatic amine is not greatly varied dependingon the length of the hydrocarbon, and the difference between a pKa valueof a Bronsted acid and a pKa value of a Bronsted base (ΔpKa) was about17 to about 18.

Example 13 Ionic Liquid 5

As described in Table 5, trifluoromethane sulfonic acid (CF₃SO₃H) wasused as the Bronsted acid, and decylamine containing a linearhydrocarbon group having 10 carbon atoms (C₁₀H₂₁NH₂) was used as theBronsted base. Ionic liquid 5 was synthesized by mixing decylamine withan equal amount of trifluoromethane sulfonic acid to thereby neutralizeit.

Example 14 Ionic Liquid 6

As described in Table 5, trifluoromethane sulfonic acid (CF₃SO₃H) wasused as the Bronsted acid, and tetradecylamine containing a linearhydrocarbon group having 14 carbon atoms (C₁₄H₂₉NH₂) was used as theBronsted base. Ionic liquid 6 was synthesized by mixing tetradecylaminewith an equal amount of trifluoromethane sulfonic acid to therebyneutralize it.

Example 15 Ionic Liquid 7

As described in Table 5, trifluoromethane sulfonic acid (CF₃SO₃H) wasused as the Bronsted acid, and eicosylamine containing a linearhydrocarbon group having 20 carbon atoms (C₂₀H₄₁NH₂) was used as theBronsted base. Ionic liquid 7 was synthesized by mixing eicosylaminewith an equal amount of trifluoromethane sulfonic acid to therebyneutralize it.

Example 16 Ionic Liquid 8

As described in Table 5, trifluoromethane sulfonic acid (CF₃SO₃H) wasused as the Bronsted acid, and oleylamine containing a linearhydrocarbon group having 18 carbon atoms (C₁₈H₃₅NH₂) was used as theBronsted base. Ionic liquid 8 was synthesized by mixing oleylamine withan equal amount of trifluoromethane sulfonic acid to thereby neutralizeit.

Example 17 Ionic Liquid 9

As described in Table 5, trifluoromethane sulfonic acid (CF₃SO₃H) wasused as the Bronsted acid, and 2-heptylundecylamine containing apartially branched linear hydrocarbon group having 18 carbon atoms(CH₃(CH₂)_(n)CH(C₇H₁₅)—NH₂) (partially branched) was used as theBronsted base. Ionic liquid 9 was synthesized by mixing2-heptylundecylamine with an equal amount of trifluoromethane sulfonicacid to thereby neutralize it.

Comparative Example 10 Comparative Ionic Liquid 4

As described in Table 5, trifluoromethane sulfonic acid (CF₃SO₃H) wasused as the Bronsted acid, and octylamine containing a linearhydrocarbon group having 8 carbon atoms (C₈H₁₇NH₂) was used as theBronsted base. Comparative ionic liquid 4 was synthesized by mixingoctylamine with an equal amount of trifluoromethane sulfonic acid tothereby neutralize it.

Comparative Example 11 Comparative Ionic Liquid 5

As described in Table 5, trifluoromethane sulfonic acid (CF₃SO₃H) wasused as the Bronsted acid, and isobutylamine containing a linearhydrocarbon group having 4 carbon atoms (C₄H₉NH₂) was used as theBronsted base. Comparative ionic liquid 4 was synthesized by mixingisobutylamine with an equal amount of trifluoromethane sulfonic acid tothereby neutralize it.

TABLE 5 Total number of Lubricating agent Aliphatic amine carbon atomsIonic liquid 5 C₁₀H₂₁NH₂ 10 Ionic liquid 6 C₁₄H₂₉NH₂ 14 Ionic liquid 7C₂₀H₄₁NH₂ 20 Ionic liquid 8 C₁₈H₃₅NH₂ 18 Ionic liquid 9 iso-C₁₈H₃₇NH₂ 18Comparative ionic C₈H₁₇NH₂ 8 liquid 4 Comparative ionic C₄H₉NH₂ 4 liquid5

Example 18

A magnetic disk was produced as described above using a lubricatingagent containing Ionic liquid 5. As described in Table 6, the CSSmeasurement result of the magnetic disk was greater than 50,000,indicating excellent durability.

Example 19

A magnetic disk was produced as described above using a lubricatingagent containing Ionic liquid 6. As described in Table 6, the CSSmeasurement result of the magnetic disk was greater than 50,000,indicating excellent durability.

Example 20

A magnetic disk was produced as described above using a lubricatingagent containing Ionic liquid 7. As described in Table 6, the CSSmeasurement result of the magnetic disk was greater than 50,000,indicating excellent durability.

Example 21

A magnetic disk was produced as described above using a lubricatingagent containing Ionic liquid 8. As described in Table 6, the CSSmeasurement result of the magnetic disk was greater than 50,000,indicating excellent durability.

Example 21

A magnetic disk was produced as described above using a lubricatingagent containing Ionic liquid 9. As described in Table 6, the CSSmeasurement result of the magnetic disk was greater than 50,000,indicating excellent durability.

Comparative Example 12

A magnetic disk was produced as described above using a lubricatingagent containing Comparative Ionic liquid 4. As described in Table 6,the CSS measurement result of the magnetic disk was 23,500.

Comparative Example 13

A magnetic disk was produced as described above using a lubricatingagent containing Comparative Ionic liquid 5. As described in Table 6,the CSS measurement result of the magnetic disk was 11,000.

TABLE 6 Lubricating agent CSS durability Example 18 Ionic liquid 5 25°C., 60% RH >50,000 Example 19 Ionic liquid 6 25° C., 60% RH >50,000Example 20 Ionic liquid 7 25° C., 60% RH >50,000 Example 21 Ionic liquid8 25° C., 60% RH >50,000 Example 22 Ionic liquid 9 25° C., 60%RH >50,000 Comparative Comparative ionic 25° C., 60% RH 23,500 Example12 liquid 4 Comparative Comparative ionic 25° C., 60% RH 11,000 Example13 liquid 5

As can be seen from Table 6, Examples 18 to 22 in which ionic liquidsformed from Bronsted bases containing a hydrocarbon having at least 10or more carbon atoms were used in magnetic disks had the CSS durabilityof greater than 50,000 times, indicating that they have superiordurabilities to Comparative Examples 12 and 13 in which ionic liquidsformed from Bronsted bases containing a hydrocarbon having 8 or lesscarbon atoms were used.

Next, Examples in which Ionic liquids 5 to 9 and Comparative ionicliquids 4 and 5 were applied to magnetic tapes will now be described.

Example 23

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 5. As described in Table 7, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.22 under the environment of a temperature of −5° C.and 0.23 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were 53 min under theenvironment of a temperature of −5° C. and longer than 60 min under theenvironment of a temperature of 40° C. and a relative humidity of 30%.The shuttle durabilities were 153 times under the environment of atemperature of −5° C. and 126 times under the environment of atemperature of 40° C. and a relative humidity of 90%. From theseresults, it has been found that the magnetic tape onto which Ionicliquid 5 was applied has excellent frictional property, stilldurability, and shuttle durability.

Example 24

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 6. As described in Table 7, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.20 under the environment of a temperature of −5° C.and 0.21 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. From these results, it has been found that the magnetic tape ontowhich Ionic liquid 6 was applied has excellent frictional property,still durability, and shuttle durability.

Example 25

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 7. As described in Table 7, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.21 under the environment of a temperature of −5° C.and 0.21 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. From these results, it has been found that the magnetic tape ontowhich Ionic liquid 7 was applied has excellent frictional property,still durability, and shuttle durability.

Example 26

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 8. As described in Table 7, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.22 under the environment of a temperature of −5° C.and 0.22 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. From these results, it has been found that the magnetic tape ontowhich Ionic liquid 8 was applied has excellent frictional property,still durability, and shuttle durability.

Example 27

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 9. As described in Table 7, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.24 under the environment of a temperature of −5° C.and 0.25 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were 51 min under theenvironment of a temperature of −5° C. and 59 min under the environmentof a temperature of 40° C. and a relative humidity of 30%. The shuttledurabilities were 135 times under the environment of a temperature of−5° C. and 158 times under the environment of a temperature of 40° C.and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 9 was applied hasexcellent frictional property, still durability, and shuttle durability.

Comparative Example 14

A magnetic tape was produced as described above using the lubricatingagent containing Comparative ionic liquid 4. As described in Table 7,the coefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.29 under the environment of a temperature of −5° C.and 0.30 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were 35 min under theenvironment of a temperature of −5° C. and 39 min under the environmentof a temperature of 40° C. and a relative humidity of 30%. The shuttledurabilities were 96 times under the environment of a temperature of −5°C. and 95 times under the environment of a temperature of 40° C. and arelative humidity of 90%.

Comparative Example 15

A magnetic tape was produced as described above using the lubricatingagent containing Comparative ionic liquid 5. As described in Table 7,the coefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.36 under the environment of a temperature of −5° C.and 0.41 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were 15 min under theenvironment of a temperature of −5° C. and 25 min under the environmentof a temperature of 40° C. and a relative humidity of 30%. The shuttledurabilities were 86 times under the environment of a temperature of −5°C. and 54 times under the environment of a temperature of 40° C. and arelative humidity of 90%.

TABLE 7 Coefficient of friction after Lubricating 100 times of StillShuttle agent shuttle runs durability/min durability Ex. 23 Ionic liquid5 −5° C.  0.22 −5° C.    53 −5° C.    153 40° C., 0.23 40° C., >60 40°C.,   126 90% RH 30% RH 90% RH Ex. 24 Ionic liquid 6 −5° C.  0.20 −5°C.  >60 −5° C.  >200 40° C., 0.21 40° C., >60 40° C., >200 90% RH 30% RH90% RH Ex. 25 Ionic liquid 7 −5° C.  0.21 −5° C.  >60 −5° C.  >200 40°C., 0.21 40° C., >60 40° C., >200 90% RH 30% RH 90% RH Ex. 26 Ionicliquid 8 −5° C.  0.22 −5° C.  >60 −5° C.  >200 40° C., 0.22 40° C., >6040° C., >200 90% RH 30% RH 90% RH Ex. 27 Ionic liquid 9 −5° C.  0.24 −5°C.    51 −5° C.    135 40° C., 0.25 40° C.,   59 40° C.,   158 90% RH30% RH 90% RH Comp. Comparative −5° C.  0.29 −5° C.    35 −5° C.     96Ex. 14 ionic liquid 4 40° C., 0.30 40° C.,   39 40° C.,    95 90% RH 30%RH 90% RH Comp. Comparative −5° C.  0.36 −5° C.    15 −5° C.     86 Ex.15 ionic liquid 5 40° C., 0.41 40° C.,   25 40° C.,    54 90% RH 30% RH90% RH

As can be seen from Table 7, Examples 23 to 27 in which ionic liquidsformed from Bronsted bases containing a hydrocarbon having at least 10or more carbon atoms were used in magnetic tapes has greatly improvedcoefficient of friction, still durability, and shuttle durability ascompared to Comparative Examples 14 and 15 in which ionic liquids formedfrom Bronsted bases containing a hydrocarbon having 8 or less carbonatoms were used. Example 26 in which the ionic liquid containing alinear hydrocarbon group having a double bound was used in the magnetictape and Example 27 in which the ionic liquid having a branchedhydrocarbon group was used in the magnetic tape had slightly highercoefficients of friction than those having 14 or more carbon atoms, buthad the still durability and the shuttle durability sufficientlysatisfying practical specification.

<3.3 Effect of Other Structures than Hydrocarbon Group in Bronsted Base>

Next, ionic liquids were synthesized using, as the Bronsted base,compounds (cyclic amidine) in which other structures than thehydrocarbon group are different from amine. Lubricating agentscontaining the ionic liquids were used in magnetic recording media toexamine an effect of other structures than the hydrocarbon group in theBronsted base.

Example 28 Synthesis of C₈F₁₇SO₃ ⁻H₃N⁺C₁₈H₃₇ (Ionic Liquid 10)

Stearylamine was dissolved in a mixed solvent of 85% by mass of n-hexaneand 15% by mass of ethanol. An equimolar amount of perfluorooctanesulfonic acid dissolved in ethanol was added thereto, followed byheating at 60° C. for 30 min. After removing the solvent,recrystallization was performed with a mixed solvent of n-hexane and asmall amount of ethanol to thereby obtain colorless crystals (C₈F₁₇SO₃⁻H₃N⁺C₁₈H₃₇).

Example 29 Synthesis of 6-pentadecyldiazabicycloundecene(6-pentadecyl-1,8-diazabicyclo[5.4.0]undec-7-ene: 6-pentadecyl DBU)

6-Pentadecyldiazabicycloundecane represented by the following StructuralFormula (1) was synthesized according to the paper by Matsumura (N.Matsumura, H. Nishiguchi, M. Okada, and S. Yoneda, J. Heterocyclic Chem.pp. 885-887, Vol/23. Issue 3 (1986)).

Synthesis of Ionic Liquid 11

The compound represented by the Structural Formula (1) which had beenobtained using the above method was dissolved in a mixed solvent of 85%by mass of n-hexane and 15% by mass of ethanol. Perfluorooctane sulfonicacid dissolved in ethanol was added thereto [95 mol % relative to thecompound represented by the Structural Formula (1)]. After removing thesolvent, the resultant was washed with n-hexane to remove an excess ofcompounds represented by the Structural Formula (1) to thereby obtainIonic liquid 11.

Comparative Example 16 Synthesis of C₇F₁₅COO⁻H₃N⁺C₁₈H₃₇ (ComparativeIonic Liquid 6)

It was synthesized according to Tribology Trans, Vol. 37, No. 1 (January1994), pp. 99-105.

Comparative Example 17 Synthesis of C₇F₁₅CH₂O⁻H₃N⁺C₁₈H₃₇ (ComparativeIonic Liquid 7)

Stearylamine and an equimolar amount of pentadecafluorooctanol weredissolved in a mixed solvent n-hexane and a small amount of ethanol,followed by heating at 60° C. for 30 min. The resultant was filtered toremove contaminants, followed by recrystallization to thereby obtaincolorless crystals.

Table 8 shows the pKa values of the Bronsted acids, the pKa values ofthe Bronsted base, and ΔpKa values in ionic liquids obtained in Examples28 and 29 and Comparative Examples 16 and 17.

TABLE 8 Structural Formula of pKa of pKa of Bronsted acid Bronsted baseBronsted acid Bronsted base ΔpKa Example 28 C₈F₁₇SO₃H Stearylamine −3.310.7 14 Example 29 C₈F₁₇SO₃H 6-pentadecyl −3.3 12.5 15.8 DBU ComparativeC₇F₁₅COOH Stearylamine 3.8 10.7 6.9 Example 16 Comparative C₇F₁₅CH₂OHStearylamine 7-9 10.7 1.7-3.7 Example 17

<Result of Thermal Analysis>

Ionic liquids obtained from Examples 2, 28, and 29 and ComparativeExamples 16 and 17 were subjected to a TG measurement using EXSTAR 6000(Seiko Instruments Inc.) (Examples 30 and 31, and Comparative Examples18 and 19). Z-DOL was also subjected to the TG measurement (ComparativeExample 20). Weight loss was measured while purging air in a temperaturerange of 30° C. to 600° C. at a heating rate of 10° C./min. Results areshown in FIG. 4. Also, 10% weight loss temperatures are summarized inTable 9.

Note that, exothermic peak temperatures in a differential thermalanalysis (DTA) measurement of Ionic liquid 2 were 374° C. and 380° C.,and exothermic peak temperatures in the differential thermal analysis(DTA) measurement of Ionic liquid 10 were 383° C. and 402° C.

TABLE 9 10% weight loss Lubricating agent temperature/° C. Example 30Ionic liquid 10 327 Example 31 Ionic liquid 11 372 ComparativeComparative ionic 205 Example 18 liquid 6 Comparative Comparative ionic62 Example 19 liquid 7 Comparative Z-DOL 165 Example 20

From these results, it has been found that Ionic liquids 10 and 11having the ΔpKa of much greater than 7 have very high 10% weight losstemperatures. In particular, the latter has been found to have the 10%weight loss temperature 200° C. or more higher than that of Z-DOL. InIonic liquid 11, a DBU derivative having high basic strength was used asthe Bronsted base instead of stearylamine, so that the ΔpKa wasincreased and the 10% weight loss temperature was increased by 45° C. Incontrast, Comparative ionic liquid 6 having the ΔpKa of 6.9 had the 10%weight loss temperature of 205° C., and Comparative ionic liquid 7having the ΔpKa of 4 or less had the 10% weight loss temperature of 62°C., indicating poor thermal resistance.

Examples 32 and 33, and Comparative Examples 21 to 23

Next, Examples applied to metallic thin film type magnetic recordingmedia (magnetic disks) will now be described.

Magnetic disks were produced as described above using lubricating agentscontaining ionic liquids described in Table 10. The thus producedmagnetic disks were subjected to the CSS durability test and the CSSdurability test after the heating. Results are shown in Table 10.

TABLE 10 Lubricating agent CSS durability CSS durability after heatingtest Example 32 Ionic liquid 10 25° C., 60% RH >50,000 25° C., 60%RH >50,000 Example 33 Ionic liquid 11 25° C., 60% RH >50,000 25° C., 60%RH >50,000 Comparative Comparative ionic 25° C., 60% RH >50,000 25° C.,60% RH 891 Example 21 liquid 6 Comparative Comparative ionic 25° C., 60%RH >50,000 25° C., 60% RH 156 Example 22 liquid 7 Comparative Z-DOL 25°C., 60% RH >50,000 25° C., 60% RH 12,000 Example 23

As can be seen from Table 10, in Examples 32 and 33, each sample disks,which were produced by applying the ionic liquid, serving as thelubricating agent, formed from the Bronsted acid and the Bronsted basecontaining a linear hydrocarbon group having 10 or more carbon atoms andhaving the ΔpKa of 12 or more onto a carbon protecting layer formed onthe surface of the metal magnetic thin film, have excellent CSS propertyand improved durability, and these properties are maintained even afterthe heating. When the ΔpKa is less than 10, the durability after theheating is deteriorated. It is believed that this is because ionicdissociation and decomposition proceed at the high temperature tothereby deteriorate thermal stability.

Examples 34 and 35, Comparative Examples 24 to 26

Next, Examples applied to magnetic tapes will now be described.

Magnetic tapes were produced as described above using the lubricatingagents containing ionic liquids described in Table 11. The thus producedmagnetic tapes were examined for the coefficient of friction after 100times of shuttle runs, the still durability, the shuttle durability, thestill durability after the heating, and the shuttle durability after theheating. Results are shown in Table 11.

TABLE 11 Coefficient of friction after Shuttle Still durability ShuttleLubricating 100 times of Still durability/ after durability after agentshuttle runs durability/min times heating/min heating/times Ex. 34 Ionicliquid 10 −5° C.  0.19 −5° C.  >60 −5° C.  >200 −5° C.  >60 −5° C.  >20040° C., 0.23 40° C., >60 40° C., >200 40° C., >60 40° C., >200 90% RH30% RH 90% RH 30% RH 90% RH Ex. 35 Ionic liquid 11 −5° C.  0.2  −5°C.  >60 −5° C.  >200 −5° C.  >60 −5° C.  >200 40° C., 0.23 40° C., >6040° C., >200 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 30% RH 90% RHComp. Comparative −5° C.  0.22 −5° C.  >60 −5° C.  >200 −5° C.    45 −5°C.    130 Ex. 24 ionic liquid 6 40° C., 0.25 40° C., >60 40° C., >20040° C.,   36 40° C.,   123 90% RH 30% RH 90% RH 30% RH 90% RH Comp.Comparative −5° C.  0.23 −5° C.  >60 −5° C.  >200 −5° C.    12 −5° C.    30 Ex. 25 ionic liquid 7 40° C., 0.26 40° C., >60 40° C., >200 40°C.,   16 40° C.,    23 90% RH 30% RH 90% RH 30% RH 90% RH Comp. Z-DOL−5° C.  0.28 −5° C.    12 −5° C.     59 −5° C.    12 −5° C.     46 Ex.26 40° C., 0.3  40° C.,   48 40° C.,   124 40° C.,   15 40° C.,    5890% RH 30% RH 90% RH 30% RH 90% RH

In these results, the magnetic tape onto which the ionic liquid formedfrom the Bronsted acid and the Bronsted base containing a linearhydrocarbon group having 10 or more carbon atoms, and having the ΔpKa of12 or more was applied as the lubricating agent showed excellent wearresistance, still durability, and shuttle durability. However, thosehaving the ΔpKa of 7 or less, which were presented as ComparativeExamples, were greatly deteriorated in durability as with theaforementioned disks.

Example 36 Ionic Liquid 12 Synthesis ofn-octadecylamine-bistrifluoromethane sulfonylimide salt

The synthetic scheme is shown below.

Synthesis of n-octadecylamine-bisnonafluorobutane sulfonylimide salt wasperformed with reference to the paper by Huang et al. (Non-patentliterature: ing-Fang Huang, Huimin Luo, Chengdu Liang, I-Wen Sun, GaryA. Baker, and Sheng Dai, “Hydrophobic Bronsted Acid-Base Ionic LiquidsBased on PAMAM Dendrimers with High Proton Conductivity and BluePhotoluminescence,” J. Am. Chem. Soc. Vol. 127, 12784-12785 (2005)).

Firstly, 15.18 g of n-octadecylamine was dissolved in ethanol, and 60%concentrated nitric acid (d=1.360) was added dropwise thereto whilestirring. When reaching the point of neutralization, the addition wasterminated. After cooling, precipitated crystals were filtered, followedby drying to thereby obtain n-octadecylamine nitrate.

Next, 6.80 g of n-octadecylamine nitrate was dissolved in ethanol, and5.91 g of bistrifluoromethane sulfoimide lithium salt dissolved inethanol was added dropwise thereto. After the completion of titration,the resultant was stirred for 1 hour and heated under reflux for 1 hour.The resultant was cooled, followed by removing the solvent therefrom,adding water and diethyl ether thereto, separating an organic layer, andwashing the organic layer with water. The organic layer was dried overanhydrous magnesium sulfate, followed by removing the solvent therefrom,and recrystallizing from n-hexane to thereby obtainn-octadecylamine-bistrifluoromethanesulfonylimide salt (colorlesscrystals, melting point: 67° C.). FTIR spectra and TG/DTA thereof areshown in FIGS. 5 and 6.

In this Example, the FTIR measurement was performed by a transmissionmethod (e.g., a KBr plate method or a KBr tablet method) using FT/IR-460(manufactured by JASCO Corporation). Resolution was set to 4 cm⁻¹.

The TG/DTA measurement was performed in a temperature range of 30° C. to600° C. at a heating rate of 10° C./min while introducing air at a flowrate of 200 mL/min using EXSTAR 6000 (manufactured by Seiko InstrumentsInc.). As a gas chromatography mass spectrometer, 6890/5975 MSD(manufactured by Agilent Technologies, Inc.) was used. The followingmeasurement conditions were used: column: DB-1 (15 m, diameter: 0.25 mm,membrane thickness: 0.1 μm); injection temperature: 280° C.; columntemperature: initial temperature of 40° C., hold for 5 min, heated to340° C. at the heating rate of 20° C./min, and hold at the sametemperature; mass spectrometric unit: 5975MSD; MS detection mode: EI⁺;quadrupole temperature: 150° C.; ion source temperature: 300° C.; massscanning range: m/z 33-700; and calibration: PFTBA.

IR absorption wavenumbers and attributes thereof are shown in Table 12.The symmetric stretching vibration of S—N—S bond was observed at 1,038cm⁻¹, the symmetric stretching vibration of SO₂ bond was observed at1,131 cm⁻¹, the symmetric stretching vibration of CF₃ was observed at1,194 cm⁻¹, the anti-symmetric stretching vibration of SO₂ bond wasobserved at 1,344 cm⁻¹, the anti-symmetric deformation vibration of NH₄⁺ was observed at 1,600 cm⁻¹, the symmetric stretching vibration of CH₂was observed at 2,850 cm⁻¹, the anti-symmetric stretching vibration ofCH₂ was observed at 2,916 cm⁻¹, and the broad symmetric stretchingvibration of NH₄ ⁺ was observed at 3,360 cm⁻¹ to 3,020 cm⁻¹. Based onthese results, the structure of the resultant compound was determined.

Additionally, TG/DTA showed that the 10% weight loss temperature wasvery high of 329° C. and the weight loss was exothermic, suggesting thatthe weight loss is resulted from decomposition reaction of the compound.

TABLE 12 Band Assignment 1,038 cm⁻¹ ν_(as)*SNS 1,131 cm⁻¹ ν_(s)**SO₂1,194 cm⁻¹ ν_(s)CF₃ 1,344 cm⁻¹ ν_(as)SO₂ 1,600 cm⁻¹ σ_(as)***NH₄ ⁺ 2,850cm⁻¹ ν_(a)CH₂ 2,916 cm⁻¹ ν_(as)CH₂ 3,360 cm⁻¹ to 3,020 cm⁻¹ ν_(s)NH₄ ⁺

Example 37 Ionic Liquid 13 Synthesis ofn-octadecylamine-bisnonafluorobutane sulfonylimide salt

The synthetic scheme is shown below.

Bisnonafluorobutane sulfonylimide (9.31 g) was dissolved in ethanol, andn-octadecylamine dissolved in ethanol was added thereto. After heatingunder reflux for 30 min, the solvent was removed. Recrystallization fromn-hexane was performed to thereby obtainn-octadecylamine-bisnonafluorobutane sulfonylimide salt (colorlesscrystals, melting point: 118° C.). FTIR spectra and TG/DTA thereof areshown in FIGS. 7 and 8.

IR absorption wavenumbers and attributes thereof are shown in Table 13.The symmetric stretching vibration of S—N—S bond was observed at 1,031cm⁻¹, the symmetric stretching vibration of SO₂ bond was observed at1,088 cm⁻¹, the symmetric stretching vibration of CF₃ and CF₂ wereobserved at 1,200 cm⁻¹ and 1,141 cm⁻¹, the anti-symmetric stretchingvibration of SO₂ bond was observed at 1,355 cm⁻¹, the anti-symmetricdeformation vibration of NH₄ ⁺ was observed at 1,616 cm⁻¹, the symmetricstretching vibration of CH₂ was observed at 2,856 cm⁻¹, theanti-symmetric stretching vibration of CH₂ was observed at 2,926 cm⁻¹,and the broad symmetric stretching vibration of NH₄ ⁺ was observed at3,360 cm⁻¹ to 3,025 cm⁻¹. Based on these results, the structure of theresultant compound was determined.

Additionally, TG/DTA showed that the 10% weight loss temperature wasvery high of 331° C. and the weight loss was exothermic in this case aswell, suggesting that the weight loss is resulted from decompositionreaction of the compound.

TABLE 13 Band Assignment 1,031 cm⁻¹ ν_(as)SNS 1,088 cm⁻¹ ν_(s)SO₂ 1,200cm⁻¹, 1,141 cm⁻¹ ν_(s)CF₂, ν_(s)CF₃ 1,355 cm⁻¹ ν_(a)SO₂ 1,616 cm⁻¹σ_(as)NH₄ ⁺ 2,856 cm⁻¹ ν_(a)CH₂ 2,926 cm⁻¹ ν_(as)CH₂ 3,360 cm⁻¹ to 3,025cm⁻¹ ν_(s)NH₄ ⁺

Example 38 Ionic Liquid 14 Synthesis ofn-octadecylamine-cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide salt

The synthetic scheme is shown below.

Cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide (5.45 g) was dissolved inethanol, and n-octadecylamine (5 g) dissolved in ethanol was addedthereto. Heat was generated, so that a periphery therearound was cooledwith ice. After heating under reflux for 30 min, the solvent wasremoved. Recrystallization from n-hexane was performed to thereby obtainn-octadecylamine-cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide salt(colorless crystals, melting point: 92° C.). FTIR spectra and TG/DTAthereof are shown in FIGS. 9 and 10.

IR absorption wavenumbers and attributes thereof are shown in Table 14.The symmetric stretching vibration of S—N—S bond was observed at 1,043cm⁻¹, the symmetric stretching vibration of SO₂ bond was observed at1,096 cm⁻¹, the symmetric stretching vibration of F₂ were observed at1,188 cm⁻¹ and 1,154 cm⁻¹, the anti-symmetric stretching vibration ofSO₂ bond was observed at 1,348 cm⁻¹, the anti-symmetric deformationvibration of NH₄ ⁺ was observed at 1,608 cm⁻¹, the symmetric stretchingvibration of CH₂ was observed at 2,850 cm⁻¹, the anti-symmetricstretching vibration of CH₂ was observed at 2,920 cm⁻¹, and the broadsymmetric stretching vibration of NH₄ ⁺ was observed at 3,350 cm⁻¹ to3,035 cm⁻¹. Based on these results, the structure of the resultantcompound was determined.

Additionally, TG/DTA showed that the 10% weight loss temperature wasvery high of 347° C. and the weight loss was exothermic in this case aswell, suggesting that the weight loss is resulted from decompositionreaction of the compound.

TABLE 14 Band Assignment 1,043 cm⁻¹ ν_(as)SNS 1,096 cm⁻¹ ν_(s)SO₂ 1,154cm⁻¹, 1,188 cm⁻¹ ν_(s)CF₂ 1,348 cm⁻¹ ν_(a)SO₂ 1,608 cm⁻¹ σ_(as)NH₄ ⁺2,850 cm⁻¹ ν_(a)CH₂ 2,920 cm⁻¹ ν_(as)CH₂ 3,350 cm⁻¹ to 3,035 cm⁻¹ν_(s)NH₄ ⁺

Example 39 Ionic Liquid 15 Synthesis of6-n-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene (C18-DBU)pentadecafluorooctane sulfonic acid salt

The synthetic scheme of C18-DBU is shown below.

C18-DBU was synthesized with reference to the method by Matsumura et al.(Non-patent literature: Noboru Matsumura, Hiroshi Nishiguchi, MasaoOkada, and Shigeo Yoneda, “Preparation and Characterization of6-Substituted 1,8-diazabicyclo[5.4.0]undec-7-ene,” J. HeterocyclicChemistry Vol. 23, Issue 3, pp. 885-887 (1986)).

Firstly, 7.17 g of 1,8-diazabicyclo[5.4.0]-7-undecene (DBU), which was araw material, was dissolved in a tetrahydrofuran (THF) solution,followed by cooling to 0° C., adding dropwise 29 cc of n-butyl lithium(1.64 mol/L) thereto under an argon gas atmosphere, and stirring at 0°C. for 1 hour. To the resultant solution, was added dropwise 15.71 g ofoctadecyl bromide dissolved in THF, followed by leaving to stand withstirring for 24 hours. Note that, THF was dried over type 4A molecularsieves, and then purified by distillation, which was used immediatelythereafter. Then, the resultant was acidified with hydrochloric acid,followed by removing the solvent and dissolving in hexane. The resultantwas purified by column chromatography using aminated silica gel tothereby obtain a colorless crystal product (yield: 90%).

The thus synthesized product was confirmed to be the intended compoundC18-DBU by gas chromatography and mass spectrometry.

Note that, the peak at retention time of 17 min in the gaschromatography had the area ratio of 99.5%.

Next, the synthetic scheme of C18-DBU pentadecafluorooctane sulfonicacid salt is shown below.

C18-DBU (3.00 g) and heptadecafluorooctane sulfonic acid (C₈F₁₇SO₃H)(3.71 g) were dissolved in ethanol with heat, followed by removing thesolvent, and recrystallizing from a mixed solvent of n-hexane andethanol to thereby obtain colorless crystals (melting point: 41° C.).

Results of FTIR and TG/DTA are shown in FIGS. 11 and 12.

IR absorption wavenumbers and attributes thereof are shown in Table 15.The symmetric stretching vibration of CF₃ and CF₂ were observed at 1,252cm⁻¹, the stretching vibration of C═N bond was observed at 1,643 cm⁻¹,the symmetric stretching vibration of CH₂ was observed at 2,851 cm⁻¹,the anti-symmetric stretching vibration of CH₂ was observed at 2,920cm⁻¹, and the broad symmetric stretching vibration of NH⁺ was observedat 3,410 cm⁻¹ to 3,178 cm⁻¹. Based on these results, the structure ofthe resultant compound was determined.

Additionally, TG/DTA showed that the 10% weight loss temperature wasvery high of 384° C. and the weight loss was exothermic in this case aswell, suggesting that the weight loss is resulted from decompositionreaction of the compound.

TABLE 15 Band Assignment near 1,252 cm⁻¹ ν_(s)CF₂, ν_(s)CF₃ 1,643 cm⁻¹νC═N 2,851 cm⁻¹ ν_(a)CH₂ 2,920 cm⁻¹ ν_(as)CH₂ 3,410 cm⁻¹ to 3,178 cm⁻¹ν_(s)NH⁺

Example 40 Ionic Liquid 16 Synthesis of C18-DBUcyclo-hexafluoropropane-1,3-bis(sulfonyl)imide salt

The synthetic scheme of C18-DBUcyclo-hexafluoropropane-1,3-bis(sulfonyl)imide salt is shown below.

C18-DBU (3.00 g), which was synthesized in the same manner as in Example39, and cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide (2.18 g) weredissolved in ethanol, followed by heating under reflux for 30 min,removing the solvent, and recrystallizing from n-hexane to therebyobtain colorless crystals (melting point: 52° C.).

Results of FTIR and TG/DTA are shown in FIGS. 13 and 14.

IR absorption wavenumbers and attributes thereof are shown in Table 16.The symmetric stretching vibration of S—N—S bond was observed at 1,042cm⁻¹, the symmetric stretching vibration of SO₂ bond was observed at1,091 cm⁻¹, the symmetric stretching vibration of CF₂ was observed at1,164 cm⁻¹, the anti-symmetric stretching vibration of SO₂ bond wasobserved at 1,360 cm⁻¹, the stretching vibration of C═N was observed at1,633 cm⁻¹, the symmetric stretching vibration of CH₂ was observed at2,848 cm⁻¹, the anti-symmetric stretching vibration of CH₂ was observedat 2,920 cm⁻¹, and the broad symmetric stretching vibration of NH⁺ wasobserved at 3,387 cm⁻¹. Based on these results, the structure of theresultant compound was determined.

Additionally, TG/DTA showed that the 10% weight loss temperature wasvery high of 386° C. and the weight loss was exothermic in this case aswell, suggesting that the weight loss is resulted from decompositionreaction of the compound.

TABLE 16 Band Assignment 1,042 cm⁻¹ ν_(a)SNS 1,091 cm⁻¹ ν_(s)SO₂ 1,164cm⁻¹ ν_(s)CF₂ 1,360 cm⁻¹ ν_(a)SO₂ 1,633 cm⁻¹ νC═N 2,848 cm⁻¹ ν_(a)CH₂2,920 cm⁻¹ ν_(as)CH₂ 3,387 cm⁻¹ ν_(s)NH⁺

Example 41 Ionic Liquid 17 Synthesis of7-n-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decene (C18-TBD)pentadecafluorooctane sulfonic acid salt

Firstly, the synthetic scheme of7-n-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decene (C18-TBD), which is araw material, is shown below.

It was synthesized with reference to the method by R. W. Alder et al.(Non-patent literature: Roger W. Alder, Rodney W. Mowlam, David J.Vachon and Gray R. Weisman, “New Synthetic Routes to MacrocyclicTriamines,” J. Chem. Sos. Chem. Commun. pp. 507-508 (1992)).

That is, sodium hydride (55% by mass hexane) was added at 10° C. to 8.72g of 1,5,7-triazabicyclo[4.4.0]-5-decene (TBD), which was produced inthe same manner as in Example 39, dissolved in dry THF, followed bystirring. While maintaining the temperature at 10° C., octadecanebromide was added dropwise thereto for 20 min, followed by stirring for30 min at that temperature and 2 hour at room temperature, and heatingunder reflux for 1 hour. The resultant was cooled to room temperature,and then an excess of sodium hydride was allowed to react with theaddition of ethanol. The solvent was removed therefrom and the resultantwas subjected to column chromatography using aminated silica gel tothereby obtain the intended light yellow product.

The thus synthesized product was confirmed to be the intended compoundC18-TBD (molecular weight: 391) by gas chromatography and massspectrometry.

Note that, in the gas chromatography, impurities from the solvent wasobserved at 10.5 min, but the peak at retention time of 17 min had thearea ratio of 98%.

Next, the synthetic scheme of C18-TBD pentadecafluorooctane sulfonicacid salt is shown below.

C18-TBD (3.91 g) and pentadecafluorooctane sulfonic acid (5.00 g) weredissolved in ethanol, followed by heating under reflux for 30 min,removing the solvent therefrom, and recrystallizing from n-hexane tothereby obtain colorless crystals (melting point: 65° C.).

IR and TG/DTA are shown in FIGS. 15 and 16.

IR absorption wavenumbers and attributes thereof are shown in Table 17.The symmetric stretching vibration of CF₃ and CF₂ was observed at near1,255 cm⁻¹, the stretching vibration of C═N was observed at 1,602 cm⁻¹,the symmetric stretching vibration of CH₂ was observed at 2,851 cm⁻¹,the anti-symmetric stretching vibration of CH₂ was observed at 2,924cm⁻¹, and the symmetric stretching vibration of NH⁺ was observed at3,289 cm⁻¹. Based on these results, the structure of the resultantcompound was determined.

Additionally, TG/DTA showed that the 10% weight loss temperature wasvery high of 381° C. and the weight loss was exothermic in this case aswell, suggesting that the weight loss is resulted from decompositionreaction of the compound.

TABLE 17 Band Assignment near 1,255 cm⁻¹ ν_(s)CF₂ 1,602 cm⁻¹ νC═N 2,851cm⁻¹ ν_(a)CH₂ 2,924 cm⁻¹ ν_(as)CH₂ 3,289 cm⁻¹ (broad) ν_(s)NH⁺

Example 42 Ionic Liquid 18 Synthesis of C18-TBDcyclo-hexafluoropropane-1,3-bis(sulfonyl)imide salt

The synthetic scheme of C18-TBDcyclo-hexafluoropropane-1,3-bis(sulfonyl)imide salt is shown below.

C18-TBD (4.00 g), which was synthesized in the same manner as in Example41, and hexafluoropropanesulfonylimide (3.00 g) were dissolved inethanol, followed by heating under reflux for 30 min, removing thesolvent therefrom, and recrystallizing from a mixed solvent of n-hexaneand ethanol to thereby obtain colorless crystals (melting point: 67°C.).

Results of FTIR and TG/DTA are shown in FIGS. 17 and 18.

IR absorption wavenumbers and attributes thereof are shown in Table 18.The symmetric stretching vibration of S—N—S bond was observed at 1,042cm⁻¹, the symmetric stretching vibration of SO₂ bond was observed at1,092 cm⁻¹, the symmetric stretching vibration of CF₂ was observed at1,157 cm⁻¹, the anti-symmetric stretching vibration of SO₂ bond wasobserved at 1,361 cm⁻¹, the stretching vibration of C═N was observed at1,628 cm⁻¹, the symmetric stretching vibration of CH₂ was observed at2,849 cm⁻¹, the anti-symmetric stretching vibration of CH₂ was observedat 2,921 cm⁻¹, and the symmetric stretching vibration of NH⁺ wasobserved at 3,412 cm⁻¹. Based on these results, the structure of theresultant compound was determined.

Additionally, TG/DTA showed that the 10% weight loss temperature wasvery high of 380° C. and the weight loss was exothermic in this case aswell, suggesting that the weight loss is resulted from decompositionreaction of the compound.

TABLE 18 Band Assignment 1,042 cm⁻¹ ν_(a)SNS 1,092 cm⁻¹ ν_(s)SO₂ 1,157cm⁻¹ ν_(s)CF₂ 1,361 cm⁻¹ ν_(a)SO₂ 1,628 cm⁻¹ νC═N 2,849 cm⁻¹ ν_(a)CH₂2,921 cm⁻¹ ν_(as)CH₂ 3,412 cm⁻¹ ν_(s)NH⁺

Comparative Example 27 Comparative Ionic Liquid 8 Synthesis of DBUpentadecafluorooctane sulfonic acid salt

The synthetic scheme of DBU pentadecafluorooctane sulfonic acid salt isshown below.

DBU was used as received from Tokyo Chemical Industry Co., Ltd. withoutfurther purification. DBU (5.00 g) and pentadecafluorooctane sulfonicacid (1.52 g) were dissolved in ethanol, followed by heating underreflux for 30 min, removing the solvent therefrom, and recrystallizingfrom a mixed solvent of n-hexane and ethanol to thereby obtain colorlesscrystals (melting point: 121° C.).

Results of FTIR and TG/DTA are shown in FIGS. 19 and 20.

IR absorption wavenumbers and attributes thereof are shown in Table 19.The symmetric stretching vibration of CF₃ and CF₂ was observed at near1,282 cm⁻¹, the stretching vibration of C═N was observed at 1,651 cm⁻¹,the symmetric stretching vibration of CH₂ was observed at 2,868 cm⁻¹,the anti-symmetric stretching vibration of CH₂ was observed at 2,943cm⁻¹, and the broad symmetric stretching vibration of NH⁺ was observedat 3,289 cm⁻¹. Based on these results, the structure of the resultantcompound was determined.

Additionally, TG/DTA showed that the 10% weight loss temperature wasvery high of 393° C. and the weight loss was exothermic in this case aswell, suggesting that the weight loss is resulted from decompositionreaction of the compound.

TABLE 19 Band Assignment 1,282 cm⁻¹ ν_(s)CF₂ 1,651 cm⁻¹ νC═N 2,868 cm⁻¹ν_(a)CH₂ 2,943 cm⁻¹ ν_(as)CH₂ 3,289 cm⁻¹ ν_(s)NH⁺

Comparative Example 28 Comparative Ionic Liquid 9 Synthesis of TBDpentadecafluoro sulfonic acid salt

TBD was used as received from Tokyo Chemical Industry Co., Ltd. withoutfurther purification. The synthetic scheme of TBD pentadecafluorosulfonic acid salt is shown below.

TBU (1.50 g) and pentadecafluorooctane sulfonic acid (5.39 g) weredissolved in ethanol, followed by heating under reflux for 30 min,removing the solvent therefrom, and recrystallizing from n-hexane tothereby obtain colorless crystals (melting point: 84° C.).

FTIR and TG/DTA are shown in FIGS. 21 and 22.

IR absorption wavenumbers and attributes thereof are shown in Table 20.The symmetric stretching vibration of CF₃ and CF₂ was observed at 1,202cm⁻¹ and 1,247 cm⁻¹, the stretching vibration of C═N was observed at1,633 cm⁻¹, the symmetric stretching vibration of CH₂ was observed at2,876 cm⁻¹, the anti-symmetric stretching vibration of CH₂ was observedat 2,933 cm⁻¹, and the symmetric stretching vibration of NH⁺ wasobserved at 3,040 cm⁻¹ to 3,629 cm⁻¹. Based on these results, thestructure of the resultant compound was determined.

Additionally, TG/DTA showed that the 10% weight loss temperature wasvery high of 371° C. and the weight loss was exothermic in this case aswell, suggesting that the weight loss is resulted from decompositionreaction of the compound.

TABLE 20 Band Assignment 1,247 cm⁻¹, 1,202 cm⁻¹ ν_(s)CF₃ and ν_(s)CF₂1,633 cm⁻¹ νC═N 2,876 cm⁻¹ ν_(a)CH₂ 2,933 cm⁻¹ ν_(as)CH₂ 3,040 cm⁻¹ to3,629 cm⁻¹ ν_(s)NH⁺

Synthesized ionic liquids are summarized in the following Table 21.

TABLE 21 Exothermic peak temperature in DTA 10% weight loss Melting NameCompound measurement/° C. temperature/° C. point/° C. ΔpKa Ionic liquid12 n-octadecylamine- 400, 422 329 67 17.9 (Ex. 36) bistrifluoromethanesulfonimide salt Ionic liquid 13 n-octadecylamine- 400, 438 331 118 18.3(Ex. 37) bisnonafluorobutane sulfonimide salt Ionic liquid 14n-octadecylamine-cyclo- 417 347 92 19.2 (Ex. 38) hexafluoropropane-1,3-bis(sulfonyl)imide salt Ionic liquid 15 C18-DBU 434, 468 384 41 23.6(Ex. 39) Pentadecafluorooctane sulfonic acid salt Ionic liquid 16C18-DBU 474 386 52 25.2 (Ex. 40) cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide Ionic liquid 17 C18-TBD 412, 444 381 65 24.8 (Ex.41) Pentadecafluorooctane sulfonic acid salt Ionic liquid 18 C18-TBD410, 480 380 67 26.4 (Ex. 42) cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide Comparative DBU 432 393 121 23.6 ionic liquid 8Pentadecafluorooctane (Comp. Ex. 27) sulfonic acid salt Comparative TBD425 371 84 24.8 ionic liquid 9 Pentadecafluorooctane (Comp. Ex. 28)sulfonic acid salt

The ionic liquids synthesized in Examples 36 to 42 were determined asIonic liquids 12 to 18. The ionic liquids synthesized in ComparativeExamples 27 and 28 were determined as Comparative ionic liquids 8 and 9.The 10% weight loss temperatures thereof are also described.

The ionic liquids synthesized herein including Comparative ionic liquidshave a high decomposition temperature and the 10% weight losstemperature of 320° C. or higher because of ΔpKa between the acid andthe base of 12 or more.

Example 43

A magnetic disk was produced as described above using a lubricatingagent containing n-octadecylamine-bistrifluoromethane sulfonylimide saltwhich is [Ionic liquid 12]. As described in Table 23, the CSSmeasurement result of the magnetic disk was greater than 50,000, and theCSS measurement result after the heating test was also greater than50,000, indicating excellent durability.

Example 44

A magnetic disk was produced as described above using a lubricatingagent containing n-octadecylamine-bisnonafluorobutane sulfonylimide saltwhich is [Ionic liquid 13]. As described in Table 23, the CSSmeasurement result of the magnetic disk was greater than 50,000, and theCSS measurement result after the heating test was also greater than50,000, indicating excellent durability.

Example 45

A magnetic disk was produced as described above using a lubricatingagent containingn-octadecylamine-cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide saltwhich is [Ionic liquid 14]. As described in Table 23, the CSSmeasurement result of the magnetic disk was greater than 50,000, and theCSS measurement result after the heating test was also greater than50,000, indicating excellent durability.

Example 46

A magnetic disk was produced as described above using a lubricatingagent containing C18-DBU pentadecafluorooctane sulfonic acid salt whichis [Ionic liquid 15]. As described in Table 23, the CSS measurementresult of the magnetic disk was greater than 50,000, and the CSSmeasurement result after the heating test was also greater than 50,000,indicating excellent durability.

Example 47

A magnetic disk was produced as described above using a lubricatingagent containing C18-DBU cyclo-hexafluoropropane-1,3-bis(sulfonyl)imidesalt which is [Ionic liquid 16]. As described in Table 23, the CSSmeasurement result of the magnetic disk was greater than 50,000, and theCSS measurement result after the heating test was also greater than50,000, indicating excellent durability.

Example 48

A magnetic disk was produced as described above using a lubricatingagent containing C18-TBD pentadecafluorooctane sulfonic acid salt whichis [Ionic liquid 17]. As described in Table 23, the CSS measurementresult of the magnetic disk was greater than 50,000, and the CSSmeasurement result after the heating test was also greater than 50,000,indicating excellent durability.

Example 49

A magnetic disk was produced as described above using a lubricatingagent containing C18-TBD cyclo-hexafluoropropane-1,3-bis(sulfonyl)imidesalt which is [Ionic liquid 18]. As described in Table 23, the CSSmeasurement result of the magnetic disk was greater than 50,000, and theCSS measurement result after the heating test was also greater than50,000, indicating excellent durability.

Comparative Example 29

A magnetic disk was produced as described above using a lubricatingagent containing DBU pentadecafluorooctane sulfonic acid salt which is[Comparative ionic liquid 8]. As described in Table 23, the CSSmeasurement result of the magnetic disk was 5,860, and the CSSmeasurement result after the heating test was 14,230. It is believedthat the coefficient of friction was increased because the lubricatingagent contained no long-chain hydrocarbon.

Comparative Example 30

A magnetic disk was produced as described above using a lubricatingagent containing TBD pentadecafluorooctane sulfonic acid salt which is[Comparative ionic liquid 9]. As described in Table 23, the CSSmeasurement result of the magnetic disk was 6,230, and the CSSmeasurement result after the heating test was 18,501. It is believedthat the coefficient of friction was increased because the lubricatingagent contained no long-chain hydrocarbon.

TABLE 23 CSS CSS durability/ durability after 25° C., heating/25° C.,Lubricating agent 60% RH 60% RH Example 43 Ionic liquid12 >50,000 >50,000 Example 44 Ionic liquid 13 >50,000 >50,000 Example 45Ionic liquid 14 >50,000 >50,000 Example 46 Ionic liquid15 >50,000 >50,000 Example 47 Ionic liquid 16 >50,000 >50,000 Example 48Ionic liquid 17 >50,000 >50,000 Example 49 Ionic liquid18 >50,000 >50,000 Comparative Comparative ionic 5,860 14,230 Example 29liquid 8 Comparative Comparative ionic 6,230 18,501 Example 30 liquid 9

As clearly can be seen from the above description, the lubricating agentcontaining the ionic liquid which consists of the Bronsted acid and theBronsted base containing a linear hydrocarbon group having at least 10or more carbon atoms and which has the difference of the pKa valuesthereof (ΔpKa) of 6 or more can maintain an excellent lubricatingproperty even under a high temperature storage condition, and canmaintain its CSS lubricating property for a long period of time.

Next, Examples applied to magnetic tapes will now be described.

Example 50

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 12. As described in Table 24, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.19 under the environment of a temperature of −5° C.and 0.23 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 12 was applied hasexcellent frictional property, still durability, and shuttle durability.

Example 51

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 13. As described in Table 24, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.20 under the environment of a temperature of −5° C.and 0.22 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 13 was applied hasexcellent frictional property, still durability, and shuttle durability.

Example 52

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 14. As described in Table 24, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.21 under the environment of a temperature of −5° C.and 0.24 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 14 was applied hasexcellent frictional property, still durability, and shuttle durability.

Example 53

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 15. As described in Table 24, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.22 under the environment of a temperature of −5° C.and 0.26 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 15 was applied hasexcellent frictional property, still durability, and shuttle durability.

Example 54

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 16. As described in Table 24, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.23 under the environment of a temperature of −5° C.and 0.26 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 16 was applied hasexcellent frictional property, still durability, and shuttle durability.

Example 55

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 17. As described in Table 24, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.24 under the environment of a temperature of −5° C.and 0.28 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 17 was applied hasexcellent frictional property, still durability, and shuttle durability.

Example 56

A magnetic tape was produced as described above using the lubricatingagent containing Ionic liquid 18. As described in Table 24, thecoefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.23 under the environment of a temperature of −5° C.and 0.27 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were longer than 60 min underthe environment of a temperature of −5° C. and longer than 60 min underthe environment of a temperature of 40° C. and a relative humidity of30%. The shuttle durabilities were greater than 200 times under theenvironment of a temperature of −5° C. and greater than 200 times underthe environment of a temperature of 40° C. and a relative humidity of90%. The still durabilities after the heating tests were longer than 60min under the environment of a temperature of −5° C. and longer than 60min under the environment of a temperature of 40° C. and a relativehumidity of 30%. The shuttle durabilities after the heating tests weregreater than 200 times under the environment of a temperature of −5° C.and greater than 200 times under the environment of a temperature of 40°C. and a relative humidity of 90%. From these results, it has been foundthat the magnetic tape onto which Ionic liquid 18 was applied hasexcellent frictional property, still durability, and shuttle durability.

Comparative Example 31

A magnetic tape was produced as described above using the lubricatingagent containing Comparative ionic liquid 8. As described in Table 24,the coefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.45 under the environment of a temperature of −5° C.and 0.49 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were 18 min under theenvironment of a temperature of −5° C. and 16 min under the environmentof a temperature of 40° C. and a relative humidity of 30%. The shuttledurabilities were 56 times under the environment of a temperature of −5°C. and 45 times under the environment of a temperature of 40° C. and arelative humidity of 90%. The still durabilities after the heating testswere 14 min under the environment of a temperature of −5° C. and 8 minunder the environment of a temperature of 40° C. and a relative humidityof 30%. The shuttle durabilities after the heating tests were 36 timesunder the environment of a temperature of −5° C. and 30 times under theenvironment of a temperature of 40° C. and a relative humidity of 90%.From these results, it has been found that the magnetic tape onto whichComparative ionic liquid 8 was applied is greatly deteriorated in thestill durability after the heating test and the shuttle durability afterthe heating test.

Comparative Example 32

A magnetic tape was produced as described above using the lubricatingagent containing Comparative ionic liquid 9. As described in Table 24,the coefficients of friction of the magnetic tapes after 100 times ofshuttle runs were 0.50 under the environment of a temperature of −5° C.and 0.55 under the environment of a temperature of 40° C. and a relativehumidity of 90%. The still durabilities were 16 min under theenvironment of a temperature of −5° C. and 14 min under the environmentof a temperature of 40° C. and a relative humidity of 30%. The shuttledurabilities were 45 times under the environment of a temperature of −5°C. and 36 times under the environment of a temperature of 40° C. and arelative humidity of 90%. The still durabilities after the heating testswere 12 min under the environment of a temperature of −5° C. and 10 minunder the environment of a temperature of 40° C. and a relative humidityof 30%. The shuttle durabilities after the heating tests were 28 timesunder the environment of a temperature of −5° C. and 25 times under theenvironment of a temperature of 40° C. and a relative humidity of 90%.From these results, it has been found that the magnetic tape onto whichComparative ionic liquid 9 was applied is greatly deteriorated in thestill durability after the heating test and the shuttle durability afterthe heating test.

TABLE 24 Coefficient of friction after Shuttle Still durability Shuttle100 times of Still durability/ after durability after shuttle runsdurability/min times heating/min heating/times Lubricating 40° C., 40°C., 40° C, 40° C., 40° C., agent −5° C. 90% RH −5° C. 30% RH −5° C. 90%RH −5° C. 30% RH −5° C. 90% RH Ex. 50 Ionic liquid 12 0.190.23 >60 >60 >200 >200 >60 >60 >200 >200 Ex. 51 Ionic liquid 13 0.20.22 >60 >60 >200 >200 >60 >60 >200 >200 Ex. 52 Ionic liquid 14 0.210.24 >60 >60 >200 >200 >60 >60 >200 >200 Ex. 53 Ionic liquid 15 0.220.26 >60 >60 >200 >200 >60 >60 >200 >200 Ex. 54 Ionic liquid 16 0.230.26 >60 >60 >200 >200 >60 >60 >200 >200 Ex. 55 Ionic liquid 17 0.240.28 >60 >60 >200 >200 >60 >60 >200 >200 Ex. 56 Ionic liquid 18 0.230.27 >60 >60 >200 >200 >60 >60 >200 >200 Comp. Comparative 0.45 0.49  18   16    56    45   14    8    36    30 Ex. 31 ionic liquid 8 Comp.Comparative 0.5 0.55   16   14    45    36   12   10    28    25 Ex. 32ionic liquid 9

The magnetic tape onto which the ionic liquid formed from the Bronstedacid and the Bronsted base containing a linear hydrocarbon group having10 or more carbon atoms, and having the ΔpKa of 12 or more in water orof 6 or more in acetonitrile was applied as the lubricating agent showedexcellent wear resistance, still durability, and shuttle durability.However, those having the ΔpKa of 12 or more in water or of 6 or more inacetonitrile, but containing no linear hydrocarbon group having 10 ormore carbon atoms, which were presented as Comparative Examples, weregreatly deteriorated in durability as with the aforementioned disks.

As clearly can be seen from the above description, the lubricating agentcontaining the ionic liquid which consists of the Bronsted acid and theBronsted base containing a linear hydrocarbon group having at least 10or more carbon atoms and which has the difference of the pKa valuesthereof (ΔpKa) of 12 or more in water or of 6 or more in acetonitrilecan maintain the lubricating property even under a high temperaturestorage condition, and can maintain the lubricating property for a longperiod of time. Therefore, the magnetic recording medium using thelubricating agent containing the ionic liquid can attain very excellentrunnability, wear resistance, and durability.

REFERENCE SIGNS LIST

-   11 Substrate-   12 Under layer-   13 Magnetic layer-   14 Carbon protecting layer-   15 Lubricating agent layer-   21 Substrate-   22 Magnetic layer-   23 Carbon protecting layer-   24 Lubricating agent layer-   25 Back coat layer

What is claimed is:
 1. A lubricating agent, comprising: an ionic liquidformed from a Bronsted acid (HX) and a Bronsted base (B), wherein theBronsted base has a linear hydrocarbon group having 10 or more carbonatoms, and wherein a difference between a pKa value of the Bronsted acidin water and a pKa value of the Bronsted base in water is 12 or more. 2.The lubricating agent according to claim 1, wherein the ionic liquid isrepresented by the following General Formula (1):

wherein at least one of R₁, R₂, R₃, and R₄ is a hydrogen atom, and atleast one of R₁, R₂, R₃, and R₄ is a group which contains the linearhydrocarbon group having 10 or more carbon atoms.
 3. The lubricatingagent according to claim 1, wherein the Bronsted base is a cyclicamidine which contains the linear hydrocarbon group having 10 or morecarbon atoms.
 4. The lubricating agent according to claim 3, wherein theionic liquid is represented by the following General Formula (2):

wherein R₁₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom in a bicyclo ring. 5.The lubricating agent according to claim 1, wherein the Bronsted acid issulfonic acid.
 6. The lubricating agent according to claim 1, whereinthe ionic liquid has an exothermic peak temperature determined by adifferential thermal analysis (DTA) measurement of 370° C. or higher. 7.The lubricating agent according to claim 1, wherein the hydrocarbongroup is an alkyl group.
 8. A lubricating agent, comprising: an ionicliquid formed from a Bronsted acid (HX) and a Bronsted base (B), whereinthe Bronsted base has a linear hydrocarbon group having 10 or morecarbon atoms, and wherein a difference between a pKa value of theBronsted acid in acetonitrile and a pKa value of the Bronsted base inacetonitrile is 6 or more.
 9. The lubricating agent according to claim8, wherein the ionic liquid is represented by the following GeneralFormula (1):

wherein at least one of R₁, R₂, R₃, and R₄ is a hydrogen atom, and atleast one of R₁, R₂, R₃, and R₄ is a group which contains the linearhydrocarbon group having 10 or more carbon atoms.
 10. The lubricatingagent according to claim 8, wherein the Bronsted base is a cyclicamidine which contains the linear hydrocarbon group having 10 or morecarbon atoms or a cyclic guanidine which contains the linear hydrocarbongroup having 10 or more carbon atoms.
 11. The lubricating agentaccording to claim 10, wherein the ionic liquid is represented by thefollowing General Formula (2) or (3):

wherein R₁₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom in a bicyclo ring,

wherein R₂₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom or a nitrogen atom in abicyclo ring.
 12. The lubricating agent according to claim 8, whereinthe ionic liquid has an exothermic peak temperature determined by adifferential thermal analysis (DTA) measurement of 370° C. or higher.13. The lubricating agent according to claim 8, wherein the Bronstedacid is perfluoroalkyl sulfonic acid, a compound represented by thefollowing Structural Formula (A), a compound represented by thefollowing Structural Formula (B), a compound represented by thefollowing Structural Formula (C), or a compound represented by thefollowing Structural Formula (D):


14. A magnetic recording medium, comprising: a non-magnetic support; andat least a magnetic layer on or above the non-magnetic support, whereinthe magnetic layer contains the lubricating agent according to claim 1.15. An ionic liquid, wherein the ionic liquid is formed from a Bronstedacid (HX) and a Bronsted base (B), wherein the Bronsted base has alinear hydrocarbon group having 10 or more carbon atoms, and wherein adifference between a pKa value of the Bronsted acid in water and a pKavalue of the Bronsted base in water is 12 or more.
 16. The ionic liquidaccording to claim 15, wherein the ionic liquid is represented by thefollowing General Formula (1):

wherein at least one of R₁, R₂, R₃, and R₄ is a hydrogen atom, and atleast one of R₁, R₂, R₃, and R₄ is a group which contains the linearhydrocarbon group having 10 or more carbon atoms.
 17. The ionic liquidaccording to claim 15, wherein the Bronsted base is a cyclic amidinewhich contains the linear hydrocarbon group having 10 or more carbonatoms.
 18. The ionic liquid according to claim 17, wherein the ionicliquid is represented by the following General Formula (2):

wherein R₁₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom in a bicyclo ring. 19.The ionic liquid according to claim 15, wherein the Bronsted acid issulfonic acid.
 20. The ionic liquid according to claim 15, wherein theionic liquid has an exothermic peak temperature determined by adifferential thermal analysis (DTA) measurement of 370° C. or higher.21. The ionic liquid according to claim 15, wherein the hydrocarbongroup is an alkyl group.
 22. The ionic liquid according to claim 15,wherein the Bronsted base is octadecylamine (C₁₈H₃₇NH₂), decylamine(C₁₀H₂₁NH₂), tetradecylamine (C₁₄H₂₉NH₂), eicosylamine (C₂₀H₄₁NH₂),oleylamine (C₁₈H₃₅NH₂), 2-heptylundecylamine (CH₃(CH₂)_(n)CH(C₇H₁₅)NH₂),or a compound represented by the following Structural Formula (1):


23. An ionic liquid, wherein the ionic liquid is formed from a Bronstedacid (HX) and a Bronsted base (B), wherein the Bronsted base has alinear hydrocarbon group having 10 or more carbon atoms, and wherein adifference between a pKa value of the Bronsted acid in acetonitrile anda pKa value of the Bronsted base in acetonitrile is 6 or more.
 24. Theionic liquid according to claim 23, wherein the ionic liquid isrepresented by the following General Formula (1):

wherein at least one of R₁, R₂, R₃, and R₁ is a hydrogen atom, and atleast one of R₁, R₂, R₃, and R₄ is a group which contains the linearhydrocarbon group having 10 or more carbon atoms.
 25. The ionic liquidaccording to claim 23, wherein the Bronsted base is a cyclic amidinewhich contains the linear hydrocarbon group having 10 or more carbonatoms or a cyclic guanidine which contains the linear hydrocarbon grouphaving 10 or more carbon atoms.
 26. The ionic liquid according to claim25, wherein the ionic liquid is represented by the following GeneralFormula (2) or (3):

wherein R₁₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom in a bicyclo ring,

wherein R₂₁ denotes the linear hydrocarbon group having 10 or morecarbon atoms and being attached to a carbon atom or a nitrogen atom in abicyclo ring.
 27. The ionic liquid according to claim 23, wherein theionic liquid has an exothermic peak temperature determined by adifferential thermal analysis (DTA) measurement of 370° C. or higher.28. The ionic liquid according to claim 23, wherein the Bronsted acid isperfluoroalkyl sulfonic acid, a compound represented by the followingStructural Formula (A), a compound represented by the followingStructural Formula (B), a compound represented by the followingStructural Formula (C), or a compound represented by the followingStructural Formula (D):


29. The ionic liquid according to claim 23, wherein the Bronsted base isoctadecylamine (C₁₈H₃₇NH₂), decylamine (C₁₀H₂₁NH₂), tetradecylamine(C₁₄H₂₉NH₂), eicosylamine (C₂₀H₄₁NH₂), oleylamine (C₁₈H₃₅NH₂),2-heptylundecylamine (CH₃(CH₂)_(n)CH(C₇H₁₅)NH₂), a compound representedby the following Structural Formula (2), or a compound represented bythe following Structural Formula (3):


30. A magnetic recording medium, comprising: a non-magnetic support; andat least a magnetic layer on or above the non-magnetic support, whereinthe magnetic layer contains the lubricating agent according to claim 8.